DDWFTTW - Tests.

[ThinAirDesigns]

If anyone DOESN’T accept that the Brennan Torpedo is an actual, practical working example of DDWFTTW (no treadmills or turntables required), that is essentially the same as the carts in the videos, ...

LOL -- yeah, "no treadmill or turntables required" -- just two motors hooked to two wire reels pulling on two cables turning two propellers underwater. That's gonna win a lot of converts. :rolleyes:

People don't even accept a DDWFTTW cart running faster than the wind in it's own environment as a working example of DDWFTTW. The Brennen Torpedo is the magic bullet of explanation :rolleyes::rolleyes:

A sailboat tacking upwind is also "an actual, practical working example of DDWFTW, but we don't seem to find a lot of folks buying into it.

I would appreciate an explanation why it isn‘t.

How about this explanation ... The Brennen Torpedo doesn't go downwind faster than the wind. Do you need more?

I suspect (but don’t know) that Spork & Co may have known about the Brennan Torpedo all along and were only here for the thrill of the “pissing match” and the limelight.

Yeah, we held out on the Sterling Silver of DDWFTTW proof -- the ever popular, widely known and absolute analogous Brennan Torpedo. We knew of course that once the word of this silver bullet proof surfaced, the limelight would be gone. I'm just so angry that you spoiled this party of ours and released this information and have used it to convince, what ... one person that it's the perfect example of DDWFTTW?

What will we do now?

JB

[ThinAirDesigns]

If Spork & Co build a “real wind” cart and travel DDWFTTW in to the limelight then it merely proves that they were after the limelight all along. Proof of the principle already exists in the Brennan Torpedo.

The above quote just keeps getting funnier and funnier:

1. Originally, Ynot doesn't believe the treadmill and wants test in 'real wind'.

2. Then he presents his infinite treadmill tests and the 'best proof ever 'for DDWFTTW

3. Then he says the the existence of the Brennen Torpedo means that if we continue with plans to execute #1, it means it *proves* that we were only after the limelight all along.

4. NOW, comes this tidbit from Ynot on another forum:

... the cart has been dismantled to use some of the bits for a small outside wind test cart I’m building ...


Ynot can't seem to figure out what sort of proof constitutes "proof" and what sort of proof proves limelight seeking. Seems in Ynot world it's fine for HIM to build an outdoor version, but if we do it's nefarious.

ROFLAO!!!

At least he's consistent in his inconsistency.

JB

[ThinAirDesigns]

In post #251, the following:
A sailboat tacking upwind is also "an actual, practical working example of DDWFTW, but we don't seem to find a lot of folks buying into it.

Should read:
A sailboat tacking upwind is also "an actual, practical working example of DWFTW, but we don't seem to find a lot of folks buying into it.

JB

[spork]

In post #251, the following:

A sailboat tacking upwind is also "an actual, practical working example of DDWFTW, but we don't seem to find a lot of folks buying into it.

Should read:

A sailboat tacking upwind is also "an actual, practical working example of DWFTW, but we don't seem to find a lot of folks buying into it.


I think you mean down-current, faster than the current. But it's clearly the same principle. And if you connected two sailboats with a telescoping pole as they tacked upwind, they would then demonstrate directly up-current faster than the current.

[ynot]

Using a variation of the Brennan Torpedo principle I have designed this as a possible directly down river faster than the river device.

It's a one-piece construction with no moving parts other than the cable. As the floating paddlewheel is taken downstream with the flow of the river it rotates off the stationary cable and “paddles” against the flow of the river, thereby travelling directly down river faster than the river. Anyone think it would it work or not?

http://www.accommodationz.co.nz/images/roller.bmp

[Dan O.]

It may either travel down river faster than the river or travel up the cable (faster than the cable that isn't moving) or it will sit in the middle moving slowly one way or the other but mostly splashing water because you are too close to a 1:1 gearing.

ETA: up cable is my guess given the dimensions in your drawing.



BTW: Brennan mentions that he got the idea for the torpedo by playing with cotton spools and found that when he pulled slowly on the thread, the spool moved away from him.

However, our demonstration with the yo-yo shows it clearly moving up the string towards the puller. How is this apparent contradiction reconciled?

[ynot]

It may either travel down river faster than the river or travel up the cable (faster than the cable that isn't moving) or it will sit in the middle moving slowly one way or the other but mostly splashing water because you are too close to a 1:1 gearing.

ETA: up cable is my guess given the dimensions in your drawing.
I agree that it all depends on the ratio of the cable spool and paddlewheel diameter as to what would happen. Are you saying that you think there is a ratio where the paddlewheel would travel directly down river faster than the river?

[ynot]

BTW: Brennan mentions that he got the idea for the torpedo by playing with cotton spools and found that when he pulled slowly on the thread, the spool moved away from him.

However, our demonstration with the yo-yo shows it clearly moving up the string towards the puller. How is this apparent contradiction reconciled?
Perhaps Brennan tested what the yoyo would do on ice ;)

ETA - Or perhaps he was pulling the string high enough above the horizontal to make the cotton reel move away.

[John Freestone]

Gosh, that's a brainteaser, ynot. Almost have to run out and find me a bridge over a river, after making one I mean. It's really hard to say, but my guess is that it would only go up cable with a much smaller cable-wind radius, and as drawn would go downstream slower than the stream. It seems to me that to do the faster thing, the vanes need to be paddling slower than the vehicle would go if it just unwound itself from the cable at waterspeed. That suggests to me that the winding radius needs to be larger than the vanes.

To avoid the thing just swinging round, you could double up the wires and have them wound round the ends, with the paddles in the middle. It still might swing from side to side, especially as it gets further from you, but your version (I guess you're just showing the principle) would be inherently unstable - any difference in force on one side will start it to turn, and it can't self-correct.

[Dan O.]

ETA - Or perhaps he was pulling the string high enough above the horizontal to make the cotton reel move away.

Your intuition serves you well. Now, how high is high enough.

[ynot]

Whether the paddlewheel rolls up (Fig1) or down (Fig3) the cable or neither (Fig2) depends if the force of the water is above or bellow the point where the cable leaves the spool. In the original picture I drew the paddlewheel would therefore roll up the cable and not down as indicated. So will this design ever be able to travel DDSFTTS? (S = Stream)

http://www.accommodationz.co.nz/images/ratios.bmp

[ynot]

Your intuition serves you well. Now, how high is high enough.
45+ degrees?

[ynot]

To avoid the thing just swinging round, you could double up the wires and have them wound round the ends, with the paddles in the middle. It still might swing from side to side, especially as it gets further from you, but your version (I guess you're just showing the principle) would be inherently unstable - any difference in force on one side will start it to turn, and it can't self-correct.
Yes, this is the way I would build it . . .

http://www.accommodationz.co.nz/images/paddlewheel.bmp

[John Freestone]

Whether the paddlewheel rolls up (Fig1) or down (Fig3) the cable or neither (Fig2) depends if the force of the water is above or bellow the point where the cable leaves the spool. In the original picture I drew the paddlewheel would therefore roll up the cable and not down as indicated. So will this design ever be able to travel DDSFTTS? (S = Stream)

http://www.accommodationz.co.nz/images/ratios.bmp
My intuition tells me that it's harder to get this to roll upstream than you think, although I can't construct a clear argument based on the forces as suggested by your drawing. It could be that this is because they are correct in perfect conditions, and my intuition is drawing on the peculiarities of real water-air-floating-object interactions. In Fig 1, for instance, if you imagine taking away the paddles, you could argue that the water is still impacting on and dragging the base of the cylinder, and that is below the cable, hence it should still wind itself up the cable, but it screams at me that it'll do no such thing and you'll be running off downstream in no time to retrieve it. That may be wrong, or it may be that in real conditions the natural changes in waves or the air currents over the water would tend to unwind it. It may seem unfair to remove the paddles and expect it to still go up-wire, but it's to make the point that there are some weird forces here. If that was fast water pulling on it, with or without it turning, a bow wave is going to ride up the upstream side, too, tending to push it downstream.

Indeed, if you put something like that in what appears to be a fairly still lake, any slight motion will unwind the cable, simply because there is a force of tension that can cause it to unwind, but you can't push a string, so it won't rewind itself very easily. In a turbulent stream, there might be some of that going on.

It's sometimes useful to think of extreme cases to see if it becomes more obvious, so what about this:

http://freedeanna.fileave.com/Diagrams/ynotspaddleup.bmp

That feels like it's got the best chance of going upstream. If we held it at the centre on an axle, of course it's just a waterwheel, and the cable does resist the force applied in a very similar fashion to a waterwheel.

I don't know if it can go DDSFTTS, or if this is the best sort of 'gear ratio':

http://freedeanna.fileave.com/Diagrams/ynotspaddledown.bmp
If you imagine the cable winders being just fairly thin wheels, joined by a long thin cylinder with fins on it, then it seems to me that the whole thing is going to be forced downstream at some fairly large fraction of water speed. My thinking is that as it does so, the vanes are forced to paddle and, although they seem to be paddling slowly by that gearing, they keep providing a little extra thrust, but maybe I've reduced them too much. I don't know. It's a little bit like the vanes on a wheel - at half the radius, a vane below the axle slows to 1/2 the speed of the wheel, so if a windcart propelled by that method has reached windspeed in a tailwind, and can't itself be pushed anymore, the vane can still gain thrust. The point at the very edge slows down to zero as it touches the ground, so a vane there could get pushed whatever speed the cart is going. Against that, there is the lever distance (being zero there), which is relatively easy to think of in the case of a mechanical wheel, but in this case it's harder. Can we think of the winding cylinder just like the wheel circumference, like the thing is rolling downstream laying cable as it goes? That seems convincing, and then my paddles here are too close to the 'axle' to be of much use. They have a great lever distance, but are moving almost at waterspeed, so the water isn't moving past them much. Yes, it looks like my first guess was a bit off. Your Fig 3 looks more likely, or perhaps somewhere between that and mine.

Interesting question. It has some strange similarities and differences to that wheel-with-vanes problem. On that, we need to get the vanes out of the way as they go forwards, so that they're not slowing the cart. Here, we aren't bothering about it so much because they're moving in air instead of water, and the water applies more pressure. However, if this thing is going at some fair old whack downstream, that might still be a problem.

What do you need it for, to send downstream faster than the stream to tell people downstream there's a crazy engineer upstream and they need to watch out for strange vehicles and taut cable coming downstream? Oh no, that would be DDSFTTV. You could warn them of floods coming, or dead goldfish. :D

[Dan O.]

45+ degrees?

I worked out what I believe is the answer when I was stringing data cables (1000' rolls of cat 6 on a spool). Someday I should draw the force diagram to verify If I am right.

[John Freestone]

It may either travel down river faster than the river or travel up the cable (faster than the cable that isn't moving) or it will sit in the middle moving slowly one way or the other but mostly splashing water because you are too close to a 1:1 gearing.

ETA: up cable is my guess given the dimensions in your drawing.



BTW: Brennan mentions that he got the idea for the torpedo by playing with cotton spools and found that when he pulled slowly on the thread, the spool moved away from him.

However, our demonstration with the yo-yo shows it clearly moving up the string towards the puller. How is this apparent contradiction reconciled?
I don't understand. Where did you get 'what Brennan said' from, and couldn't it be a typo or mistake of his own - esp. if he noticed a cotton spool coming towards the pulled cotton, but then went on to design a torpedo that went away? [ETA, the other kind being a bit dangerous!]

I'd like to read your solution for the change point to it going away.

[Dan O.]

I don't understand. Where did you get 'what Brennan said' from, and couldn't it be a typo or mistake of his own - esp. if he noticed a cotton spool coming towards the pulled cotton, but then went on to design a torpedo that went away? [ETA, the other kind being a bit dangerous!]

I'd like to read your solution for the change point to it going away.

When the Brennan torpedo was first presented, I followed the link and did some searching on my own. I'm not sure where I found that statement but it was similar to my own experience.


The transition point is easy to find. Just draw a picture of the spool with the thread being pulled at an angle. Write the equation for the motion of the thread given a motion of the spool. The transition point is where the thread doesn't move so solve the equation after substitution zero for the thread motion.

I just did this and confirmed what I already thought was the answer.

[Michael C]

When the Brennan torpedo was first presented, I followed the link and did some searching on my own. I'm not sure where I found that statement but it was similar to my own experience.

The only reference I could find is in "Nineteenth-century Torpedoes and Their Inventors (http://books.google.com/books?id=jaaHQ4FlKS4C&pg=RA1-PA154&lpg=RA1-PA154&source=bl&ots=7alVeykroN&sig=X7pDKfhmA-3TLjG-sW7HqonuZnQ&hl=en&sa=X&oi=book_result&resnum=4&ct=result)" by Edwyn Gray. Gray states that there are two stories concerning Brennan's inspiration: his colleague Robert Graham said that Brennan had the idea while musing on the way a belt-driven planing machine worked, while Norman Tomlinson (one of Brennan's first biographers) claims that it was the cotton reel:

"...Brennan had initially visuallized the concept by noting that a cotton reel, if the thread is pulled toward the operator from underneath, moves forward, not backward."

Since Tomlinson (or possibly Gray, since he doesn't quote him directly) neglects to say if "forward" means towards the operator or away from the operator, that doesn't help us much. I think it's possible that Tomlinson or somebody else made the story up: maybe Brennan used a cotton reel as an analogy to explain how the torpedo worked and this got transformed into the typical "eureka" discovery myth. I also wonder if Tomlinson or Gray had really worked out which way the cotton reel would move.

For the record, the first references to the Brennan torpedo in relation to the current DDWFTTW debates that I could find are:

- 12 December 2008: BoingBoing (http://boingboing.hexten.net/2008/12/12/downwind-faster-than-1.html#comment-355240), comment #51 from MOREHUMANTHANHUMAN, (who also says he built a version of my "down the ruler" cart but it didn't work: he must have built it wrong!)

- 15 December 2008: Rhett Allain's Dot Physics blog (http://blog.dotphys.net/2008/12/physics-and-directly-downwind-faster-than-the-wind-dwfttw-vehicles/#comment-1627), comment #29 from Jason Rogers.

[John Freestone]

When the Brennan torpedo was first presented, I followed the link and did some searching on my own. I'm not sure where I found that statement but it was similar to my own experience.


The transition point is easy to find. Just draw a picture of the spool with the thread being pulled at an angle. Write the equation for the motion of the thread given a motion of the spool. The transition point is where the thread doesn't move so solve the equation after substitution zero for the thread motion.

I just did this and confirmed what I already thought was the answer.
I used another method. Now I'm wondering what your answer is, and if I can use your method of the motion of the string. Anyway, here's my solution:

I think I'm right in saying that the angle depends on the ratios of the winding circle and the rolling circle. I get the angle from the horizontal as

sin-1(Rwind/Rroll) ... i.e. the arc-cosine of the winding radius over the rolling radius.

I figure this by drawing the continuation of the pulled cotton, the tangent it makes with the winding circle, until it intersects with the ground. If that is 'this side of' where the wheel touches, then there is a leverage in one direction (rolling it away), and if it is 'the other side of' the resting point, there is leverage in the other (rolling it towards the puller). That crossover point changes with the ratio of the radii, and the rest is just knowing your sins and cosines, which I'm embarrassed to say I had to bleedin' look up!

Is that right?

So, I've shown you mine...

[Dan O.]

Yep, that's the same answer I got. But I wonder if you actually solved it or did you just find the angle from what you thought was the answer.

My initial guess was that it had to do with the intersection of the thread force with the point of rolling contact. The proof was to calculate the motion of the thread and see that it produced the same answer.

The thread motion can be found by considering a delta rotation of the spool. Each delta radian rotation of the spool unwinds one delta thread radius of thread and moves the spool away by one delta spool radius which pulls the thread back by the sin of the angle of pull (where an angle of 0 is horizontal and pulling from the bottom of the spool).

tm = dw * tr - dw * sr * sin ( a )

setting tm = 0 and solving for a gives:

a = arcsin(tr/sr)

[Dan O.]

"...Brennan had initially visuallized the concept by noting that a cotton reel, if the thread is pulled toward the operator from underneath, moves forward, not backward."

I probably read that account in the wikipedia article. For historical reference, there is an early reference to the cotton reel origin for Brennan's idea here (http://books.google.com/books?id=c-c4AAAAMAAJ&pg=RA1-PA952&lpg=RA1-PA952&dq=brennan+cotton+reel&source=bl&ots=u_TUjtx-7Q&sig=RmMZThERcaHlA5ZI5KnOAGxuVzM&hl=en&sa=X&oi=book_result&resnum=4&ct=result#PRA1-PA952,M1) (published 1891)

[John Freestone]

Yep, that's the same answer I got. But I wonder if you actually solved it or did you just find the angle from what you thought was the answer.
Well that depends on what you consider thinking and what you consider reliable knowledge: I'm not used to all this delta rotations stuff, so for me that would require further taking apart to prove to myself. To you it is reliable knowledge. How far do we go back to first principles: aren't you just assuming that a wheel will rotate? Sines and cosines - do we go back to proving them? - etc.

I know with a fair degree of certainty that the spool, like any simple wheel, can be thought of as a lever, and that its point of contact with the ground is its fulcrum - it can't have any other as it isn't on an axle or anything. You can argue that the point where the cotton touches could also be a fulcrum, but that's just how it is with levers. As they move, the angles of the applied forces changes, so both points are a pair of fulcrums. I'm also fairly confident that I only need to consider a single position, even though the angles will change once things move.

We can therefore ignore the odd shape of the spool altogether and consider it just as a zero width and zero mass* lever between the point of contact and the point where the cotton meets it. All the rest is just 'shape' and does nothing to the conditions (if we are ignoring inertia, since we can pull arbitrarily slowly). It's then as obvious as which way a lever will move.

*The shape of the lever is such that it effectively removes the involvement of gravity. Whatever we do to that beam, it is still perfectly balanced, with no other force on it than the pull of the string and its opposite reaction. Hence the whole thing could be thought of as weightless or horizontal.

[ynot]

Regardless of how Brennan came up with the torpedo idea it was built and it worked (unless it‘s another fake moon landing conspiracy).

Every time I have measured the “stall” angle of the “cotton reel” string it has been 45 degrees to the surface. Below 45 rolls the reel towards, above 45 rolls it away.

So what way would this device roll? . . .


http://www.accommodationz.co.nz/images/rollers.bmp

[Michael C]

Every time I have measured the “stall” angle of the “cotton reel” string it has been 45 degrees to the surface. Below 45 rolls the reel towards, above 45 rolls it away.

That would indicate that the ratio of outer diameter to inner diameter is about 1.4 to 1. I'm sure that Dan and John are correct: use different shaped cotton reels, or make some reels with lego or something similar in order to test it.

So what way would this device roll? . . .

http://www.accommodationz.co.nz/images/rollers.bmp

Towards the direction of pull.

[ynot]

That would indicate that the ratio of outer diameter to inner diameter is about 1.4 to 1. I'm sure that Dan and John are correct: use different shaped cotton reels, or make some reels with lego or something similar in order to test it.
Regardless of the ratios I always get 45 degrees from the horizontal as the “stall” angle.


Towards the direction of pull.
Correct. The 45 degree angle still applies, even when the string is also taken down and under the trailing wheel.

[Dan O.]

Well that depends on what you consider thinking and what you consider reliable knowledge

I read you answer again (this time while I was awake) and agree it is a valid answer.

[John Freestone]

Regardless of the ratios I always get 45 degrees from the horizontal as the “stall” angle.Do you mean from experimenting or maths? I was surprised on drawing a few examples that there is quite a wide range of ratios that would appear to give the stall around 45 degrees. It might need to be a smaller winding circle than you might think to be very obviously different, but I haven't tested it myself. I'll try some soon. Another possible difference between the math and your results might be that the maths applies to perfect systems. Ordinary bits and bobs we make with toilet rolls and cotton act in more random ways. There is also the inertia and (once some movement occurs) momentum, and the ability of a cotton reel or similar to slide a little on most surfaces. The maths assumes that the wheel will always roll, never slide, never have any resistance to rolling, never gain any momentum, etc.



Correct. The 45 degree angle still applies, even when the string is also taken down and under the trailing wheel.Yes, I agree. It doesn't really matter what happens to the cord once it's in the bowels of the machine, is how it seems to me. What matters is the point where the force is first applied (given that there aren't other things happening, like it could tip over, etc.) - I suppose you mean that your pull end is less than the stall angle, being negative, below the horizontal. And I won't hear any of your 45 degree nonsense!

That raises another question - where the other limit is. If you increase the angle beyond the stall angle and it rolls away, then go right over the top, it will continue to roll in the same direction, although that's now towards you, but slower than you're pulling, but you could pull further and further round, even going under again. At some point it must return to the "less than stall angle". Where?

[John Freestone]

I read you answer again (this time while I was awake) and agree it is a valid answer.Thanks Dan. I consider that a great compliment. I looked at it again more carefully and was fairly confident. I'm going to get my head round yours when I get time. I can sort of see that it works, I just need to follow it properly (when I'm awake). :)

[John Freestone]

I used another method. Now I'm wondering what your answer is, and if I can use your method of the motion of the string. Anyway, here's my solution:

I think I'm right in saying that the angle depends on the ratios of the winding circle and the rolling circle. I get the angle from the horizontal as

sin-1(Rwind/Rroll) ... i.e. the arc-cosine of the winding radius over the rolling radius.

I figure this by drawing the continuation of the pulled cotton, the tangent it makes with the winding circle, until it intersects with the ground. If that is 'this side of' where the wheel touches, then there is a leverage in one direction (rolling it away), and if it is 'the other side of' the resting point, there is leverage in the other (rolling it towards the puller). That crossover point changes with the ratio of the radii, and the rest is just knowing your sins and cosines, which I'm embarrassed to say I had to bleedin' look up!

Is that right?

So, I've shown you mine...


:confused: Oh no, now I'm confused! I just noticed that I'd put "sin-1" and then "arc-cosine". I'm pretty sure it was supposed to be the arc cosine in mine. Yep, adjacent & hypot. I checked yours, Dan, and you've got arcsin! Copying my wrong answers? ;)

More coffee!

[Dan O.]

Regardless of the ratios I always get 45 degrees from the horizontal as the “stall” angle.

Try an extreme case like a round coffee tin with the plastic cap on both ends or two large wheels with a thin axle between them.


Correct. The 45 degree angle still applies, even when the string is also taken down and under the trailing wheel.

The angle comes from the rate that the string unwinds so it doesn't matter where the string goes after that as long as it doesn't upset the ballance. In the case of just the spool there is a simple mechanical construct that John pointed out.

[ynot]

Try an extreme case like a round coffee tin with the plastic cap on both ends or two large wheels with a thin axle between them.




The angle comes from the rate that the string unwinds so it doesn't matter where the string goes after that as long as it doesn't upset the ballance. In the case of just the spool there is a simple mechanical construct that John pointed out.
You are absolutely correct! 45 degrees is a delusional load of crap created by not testing at large enough ratio differences. My apologies.

ETA - And an incorrect intuition.

[John Freestone]

You are absolutely correct! 45 degrees is a delusional load of crap created by not testing at large enough ratio differences. My apologies.

ETA - And an incorrect intuition.
No problem, ynot. It's great you get stuck in and do some experimentation.

Dan, you may have missed my last post. I found that I had put sin-1 instead of cos-1, although I translated that for clarity and got the one I meant "arc-cosine" (acs). But you have the arcsin. I'd like to sort out which it is, and I want to learn your method anyway, so would you check it and give some more steps/diagram or whatever? I might've got some of my trig wrong.

Here's my working:
http://freedeanna.fileave.com/Diagrams/reelproblem1.gif
P.S. Is it still considered good practise these days to use that cos-1 notation? I think I remember being taught that because the acs, asn, sin are so easy to mix up.

[Michael C]

Dan, you may have missed my last post. I found that I had put sin-1 instead of cos-1, although I translated that for clarity and got the one I meant "arc-cosine" (acs). But you have the arcsin. I'd like to sort out which it is, and I want to learn your method anyway, so would you check it and give some more steps/diagram or whatever? I might've got some of my trig wrong.

I read through those posts a bit too fast yesterday. I think you are right: according to my calculations, the correct formula is

"angle a = arccos(tr/sr)".

I don't have time to do a complete explanation of my method now; maybe I'll manage that tomorrow.

[Dan O.]

Dan, you may have missed my last post. I found that I had put sin-1 instead of cos-1, although I translated that for clarity and got the one I meant "arc-cosine" (acs). But you have the arcsin. I'd like to sort out which it is, and I want to learn your method anyway, so would you check it and give some more steps/diagram or whatever? I might've got some of my trig wrong.

You have it right. I checked my results by assuming a horizontal pull where the coefficient is 1.0 = sin(0) :o


http://forums.randi.org/imagehosting/thum_15144497deb1365cf0.gif (http://forums.randi.org/vbimghost.php?do=displayimg&imgid=15022)

(adding extra wheels to show that it is the angle of the pulled string and not the angle where the string meets the spool)

This can be solved by either looking at forces (force pulling cart forward = horizontal component of pull on string).

Fforward = Fpull • rt / rs
Fhorizontal = Fpull • cos(a)


It can also be solved by looking at the change in length of the string given a change in position of the cart and solving for dl/dp = 0. (which will have to wait for my next post)

[John Freestone]

Wow. I don't quite grok that, but I can see how it should make sense! It's interesting to see the pull angle separated from the winding, like ynot's. It's the force forward = Fpull * rt/rs that I don't see, and then how you put them together to get the 'stall'. I can see that if Fforward = Fhorizontal, then the other bits give the final equation. That suggests that this condition is what I need to see is the solution, but I don't. It looks like Fforward should equal zero, because that's what defines the stall, unless I'm misunderstanding Fforward. Could you explain it a bit more sometime?

Glad to get the asn,acs question sorted. Looks like we both had a little nap there!

I look forward to seeing your method, too, Michael. I think I'd better go and do the empirical bit and prove it to myself. I'm a cotton-reel-come-hither virgin. :blush:

[Dan O.]

It's the force forward = Fpull * rt/rs that I don't see, and then how you put them together to get the 'stall'. I can see that if Fforward = Fhorizontal, then the other bits give the final equation. That suggests that this condition is what I need to see is the solution, but I don't. It looks like Fforward should equal zero, because that's what defines the stall, unless I'm misunderstanding Fforward. Could you explain it a bit more sometime?

Perhaps I skipped a bunch of steps. I was transfering the pull of the string to a torque on the main wheel (torque = force x distance) so we get T = Fpull • rt (the cross product is just a multiply because the force and distance are at right angles) and then convert this torque to the tangential force of the spool on the road Fforward = T/rs. But also there are a bunch of other force vectors involved that I just ignored because they all cancel out.

At each of the smaller wheels there is a pull force in the direction of the string (both ways). The torque on those wheels is balanced because the string on each side is pulling with the same force at the same radius but in opposite directions. Each segment of string between two wheels is also pulling on the cart body through the axle of the wheel but since the force is the same at both ends and in opposite directions, these forces also cancel out. The only forces on the cart that we are left with are the horizontal and vertical components of the string where it meets the first wheel and the torque on the main spool which translates into a forward pull through traction where the spool contacts the surface.

We are also making a simplifying assumption that the cart is heavy enough that the pull on the string isn't going to lift any part of it off the surface so all the vertical force vectors can simply be ignored.


ETA: Forgot to add that it is when Fforward (the force pulling the cart away) equals Fhorizontal (the force pulling the cart back), the forces acting on the cart are balanced so the cart won't move. When one of these forces is greater than the other, the cart moves in that direction.

[John Freestone]

Thank you so much Dan, that's brilliant.

Perhaps I skipped a bunch of steps. I was transfering the pull of the string to a torque on the main wheel (torque = force x distance) so we get T = Fpull • rt (the cross product is just a multiply because the force and distance are at right angles) and then convert this torque to the tangential force of the spool on the road Fforward = T/rs. But also there are a bunch of other force vectors involved that I just ignored because they all cancel out.Mostly stuff I don't know about, but I could guess the whole step made sense as one. The force trying to roll the wheel is the ratio of those radii between where we're pulling on it and its circumference. Since it's not a deformable object and we're ignoring inertia, etc., it wouldn't matter at what angle we applied the force to a wheel, it tends to roll one way or the other, so it's just the ratio of the radii. I've never worked with torque equations, but clearly they aren't too difficult in this case!

At each of the smaller wheels there is a pull force in the direction of the string (both ways). The torque on those wheels is balanced because the string on each side is pulling with the same force at the same radius but in opposite directions. Each segment of string between two wheels is also pulling on the cart body through the axle of the wheel but since the force is the same at both ends and in opposite directions, these forces also cancel out. The only forces on the cart that we are left with are the horizontal and vertical components of the string where it meets the first wheel and the torque on the main spool which translates into a forward pull through traction where the spool contacts the surface.Yes I kind of intuited that as one, but it's useful to see how you can analyse it.

We are also making a simplifying assumption that the cart is heavy enough that the pull on the string isn't going to lift any part of it off the surface so all the vertical force vectors can simply be ignored.Yes.

ETA: Forgot to add that it is when Fforward (the force pulling the cart away) equals Fhorizontal (the force pulling the cart back), the forces acting on the cart are balanced so the cart won't move. When one of these forces is greater than the other, the cart moves in that direction.I saw that this must be the missing step.

In fact, I see now that my confusion arose because it wasn't completely clear to me that the string can only cause Fforward to be to the left, no matter what angle its tangent is at within the machine. Your method of isolating the angle from the rotation makes it clear that there is no other effect at the wheel other than the ratio of the radii. To get Fforward to force the wheel to the right, we have to imagine that thread radius getting smaller and smaller until it passes the centre and pulls the other way. All we're left with for the opposing force is Fhorizontal a horizontal vector component of the external pull force, and again it is simplified by separating the two effects (rolling and pulling), because a string can't push, so we know that these two must oppose each other.

That's been very instructive for me, Dan. Cheers.

Ynot - I've just realised that your Testing thread has got very theoretical. Hope you don't mind. You started it!

[ynot]

Ynot - I've just realised that your Testing thread has got very theoretical. Hope you don't mind. You started it!

It has been a great learning exercise so thanks to Dan O and yourself for your efforts. My layman’s method is to extend the line of the string past the spool to a point on the circumference of the wheel. If this point is beyond the vertical (from the string side) it will roll up the string (backwards). If at the vertical it will stall (won’t roll) and if on the string side from the vertical it will roll off the string (forwards). Don’t think that explains what I mean very well so here’s a pic . . .

http://www.accommodationz.co.nz/images/angles.bmp


As I said earlier, this doesn’t fully apply to a paddlewheel in water because the paddlewheel is partially submerged and doesn’t run just on the surface of the water.

[ynot]

I put my TT and cart together again to show a visiting friend and made a video with the TT running at a slower speed for those that want to compare calculations at different speeds. I have also replaced the “large” tether arm with a thin bar. Are there any other tests anyone wants done while it’s together again?

http://www.youtube.com/watch?v=5wijrV-1pHw

[Dan O.]

ynot
Location: New Zealand

I should have looked at that before. Of course your cart's going to appear to be working when it spins that way. You're on the other frigg'n side of the world!! :covereyes



So, when are you going to mount the solid disk on an axle so we can see more of the ball rolling on a spinning disk?

[Michael C]

I put my TT and cart together again to show a visiting friend and made a video with the TT running at a slower speed for those that want to compare calculations at different speeds. I have also replaced the “large” tether arm with a thin bar. Are there any other tests anyone wants done while it’s together again?

http://www.youtube.com/watch?v=5wijrV-1pHw

The test already shows the cart starting from a stationary position and accelerating past wind speed. What more do the doubters want? Well, it's obvious that those who think the tether arm somehow makes the cart go forward (Humber!) won't be impressed, but perhaps you could do something for the "kinetic energy" camp. How about running exactly the same test at the same speed, but leave it going longer? Leave it going for several more minutes, so people can see that a terminal velocity is attained and held: in your video I can't work out if the cart is still accelerating at the end, or if it has already reached its terminal velocity.

Maybe for a longer test you could do a voice-over, or at least replace the nerve-grating motor sound with some suitable music?

[tsig]

The test already shows the cart starting from a stationary position and accelerating past wind speed. What more do the doubters want? Well, it's obvious that those who think the tether arm somehow makes the cart go forward (Humber!) won't be impressed, but perhaps you could do something for the "kinetic energy" camp. How about running exactly the same test at the same speed, but leave it going longer? Leave it going for several more minutes, so people can see that a terminal velocity is attained and held: in your video I can't work out if the cart is still accelerating at the end, or if it has already reached its terminal velocity.

Maybe for a longer test you could do a voice-over, or at least replace the nerve-grating motor sound with some suitable music?

Take it outside and run it in the wind. Why is that so hard for you to do?

[spork]

Take it outside and run it in the wind. Why is that so hard for you to do?

Build one and you'll see. Why is that so hard for you to do?

By the way, I'll be the first in line to tell you the thousands of things that are wrong with your demonstration when you do.

[ynot]

ynot
Location: New Zealand

I should have looked at that before. Of course your cart's going to appear to be working when it spins that way. You're on the other frigg'n side of the world!! :covereyes



So, when are you going to mount the solid disk on an axle so we can see more of the ball rolling on a spinning disk?
I did the “marble” test just to show how low friction, rolling kinetic enery could cause a thing to almost hover on a moving surface for some time (ball bearing was even better). At that stage I was concerned that the cart might be conserving kinetic energy and gradually slowing down. As my cart has run for over 10 minutes on the TT without losing any speed this concern has been answered (for me). (it doesn’t). The TT/cart designs I’m using were only meant to be test models but they work well enough (for me) that I don’t have to build better models.

[mender]

The longer I have to wait for the right conditions to test my cart outside, the more respect I have for Jack Goodman. I missed my one good opportunity by about 15 minutes and about 30 degrees of wind direction.

[ynot]

The test already shows the cart starting from a stationary position and accelerating past wind speed. What more do the doubters want? Well, it's obvious that those who think the tether arm somehow makes the cart go forward (Humber!) won't be impressed, but perhaps you could do something for the "kinetic energy" camp. How about running exactly the same test at the same speed, but leave it going longer? Leave it going for several more minutes, so people can see that a terminal velocity is attained and held: in your video I can't work out if the cart is still accelerating at the end, or if it has already reached its terminal velocity.
It takes ages to upload videos to Youtube so I keep them as short as possible. I let them run to beyond where I believe the cart has reached terminal speed. I’ve tested that terminal speed is constant for over 10 minutes. Those that say I could be lying could also say that a video showing this could be faked.

Maybe for a longer test you could do a voice-over, or at least replace the nerve-grating motor sound with some suitable music?
Or you could simply turn your sound off.

[ynot]

Here’s a video of a crude, smaller, tiered TT to change the relative speed. It was put together very quickly so “never mind the quality, feel the width”. It shows you don’t need to build a big TT to observe the effect.

http://www.youtube.com/watch?v=DWcjmQ8Vz88

(don't forget to turn your sound off ;-)

[ynot]

A smaller cart wheel (5.5cm dia). Sorry about the background glare and the now unbalanced TT (stupid tiered demo).

http://www.youtube.com/watch?v=VOlCTCrJjx8

[tsig]

Build one and you'll see. Why is that so hard for you to do?

By the way, I'll be the first in line to tell you the thousands of things that are wrong with your demonstration when you do.

You are the one making the claim not me. Why do you shift the burden of proof. Could it be that your cart doesn't work in the wind?

[mender]

tsig, it just ain't that easy to have the right wind for testing. Going downstairs and turning on the treadmill to get a consistent air/ground speed difference is.

I put in my wind order at least a month again. So far the best is a wind that started the cart moving slowly along the ground from a standstill. Kinda hard to get decent test conditions up here with all the ice and snow too.

[John Freestone]

It takes ages to upload videos to Youtube so I keep them as short as possible.Nice set of test videos ynot. Good work. Have you tried using a program to compress the videos more first? Youtube compresses them afterwards anyway, but that doesn't help you sending them. I have had some success loading mine into Windows Movie Maker (I'm using Win XP, but Vista will have something similar, and there's sure to be something for Linux too), which has various options for specifying the quality as you save. You could also put titles, dub music or voice over, etc., although
Or you could simply turn your sound off.yep, that's the option I prefer most of the time (generally, I mean - I sometimes switch it on to hear the noise on yours!). A voice over could be interesting, but I think they're fine showing what they show, and the noise is what you'd hear if you were there watching what they show.

[tsig]

tsig, it just ain't that easy to have the right wind for testing. Going downstairs and turning on the treadmill to get a consistent air/ground speed difference is.

I put in my wind order at least a month again. So far the best is a wind that started the cart moving slowly along the ground from a standstill. Kinda hard to get decent test conditions up here with all the ice and snow too.

For thousands of years the wind has been used for transportation now you tell me that it isn't consistent enough. All of you cart fanciers say the treadmill and the wind are the same. I'm just asking you to prove it.

[fredriks]

tsig, whats the problem with the outdoor tests that are already done? For example this one
http://www.youtube.com/watch?v=aJpdWHFqHm0

[Subduction Zone]

For thousands of years the wind has been used for transportation now you tell me that it isn't consistent enough. All of you cart fanciers say the treadmill and the wind are the same. I'm just asking you to prove it.

tsig, part of the problem of the outdoor test is that the speed of the wind is arguable, as is the speed of the cart. When I used to argue with spork about this on the Mythbusters forum one solution that many of us anti's suggested was that he use a treadmill. We all knew that it was a frame of reference equivalent of traveling at wind speed when the cart is maintaining belt speed. In fact much of our argument was said with some sort of nasty tone like: "if you think it'll work then why don't you build one?" Well he did, it worked, spork was right, period. The treadmill gives both a definite wind speed and an observable speed for the cart. A perfect model for this problem.

[Subduction Zone]

tsig, spork and JB also did an outdoor test, this was done only to show that the cart would take off on its own in the wind. No attempt was made to see if it actually got past wind speed, that is what the indoor tests show. http://www.youtube.com/watch?v=kWSan2CMgos

[spork]

The TT/cart designs I’m using were only meant to be test models but they work well enough (for me) that I don’t have to build better models.

The cart models we built were intended as "test models" as well. They were good enough to convince us - and many others. But we still took a load of crap from you about how we weren't building your contraption and doing your tests for you. Perhaps now you get it.

The longer I have to wait for the right conditions to test my cart outside, the more respect I have for Jack Goodman. I missed my one good opportunity by about 15 minutes and about 30 degrees of wind direction.

No doubt! The guy is riding a bike, controlling the cart via R/C, and filming - while half blind. And he's not 19 years old. I think he did an outstanding job designing and building his cart, operating it, and getting the video - not to mention finding a day and a place with a level road directly downwind for a long enough stretch to produce the video he did. I know for a fact that it took a long time to find the right place and the right day.

The bad news is this... if nothing else we've learned that any outdoor video will be held up as a hoax or improper because it's not going directly downwind, it's going downhill, the wind isn't steady, the tell-tale is not placed well... while an indoor test will be dismissed as not using "real" wind.

I would love to see your outdoor test Mender - but please don't be surprised when it convinces no one but those of us that are already convinced.

You are the one making the claim not me. Why do you shift the burden of proof.

On the contrary. It is you making the claim that inertial frames are not equivalent. That is a bold claim indeed since it's been known for several hundred years that they are. Your claim that a device can distinguish between a tailwind on a road vs. a treadmill moving beneath it would be worthy of a Nobel prize if you could prove it. So I strongly maintain that burden of proof is entirely on you.

Could it be that your cart doesn't work in the wind?

No - it couldn't. You've seen it on video, and you can see it in person.


For thousands of years the wind has been used for transportation now you tell me that it isn't consistent enough.

WRONG - it's the sceptics that are saying the wind outdoors is not consistent enough. How many thousands of posts from sceptics would you need to see to understand this.

All of you cart fanciers say the treadmill and the wind are the same. I'm just asking you to prove it.

It's been proven by Galileo, Newton, and Einstein. I need not add to their body of work.

[sol invictus]

For thousands of years the wind has been used for transportation now you tell me that it isn't consistent enough. All of you cart fanciers say the treadmill and the wind are the same. I'm just asking you to prove it.

For 500 years physicists have been saying that inertial frames are equivalent, and so the treadmill and wind are the same. Now you tell us that isn't true? I'm just asking you to prove it.

[Subduction Zone]

spork there are some people who no matter what will not believe this is possible. You can show them with ice boats real world examples of VMG greater than the wind, show how a cart could be made with two ice boats that would power a DDWFTTW cart, and they will still claim over unity for your particular design. Congrats by the way on the last youtube video. I was amazed at how fast the cart went from being pulled back by the treadmill to pulling forward when you picked it up and dropped it.

[ynot]

Meanwhile . . . back in the workshop - I’ve built a circular wind tunnel to test if DDWFTTW is possible in a “real” wind. Unfortrunately the cart travels so fast it’s not easy to video to see what’s going on. On a TT or TM the observed speed of the cart is the speed of the cart above wind speed. In “real” wind however it’s the speed of the cart above wind speed plus the speed of the wind (quite fast). So at this stage I am only able to provide photos of the results . . .

Pic 1 is the cart going slower than wind and the ribbon is angled in the direction of the wind (right to left on the “back” side as indicated by the arrow).

http://www.accommodationz.co.nz/images/slower.jpg


Pic 2 is the cart going faster than the wind and the ribbon is angled in the opposite direction to the wind. The cart is therefore going faster than the wind and in to a headwind.

http://www.accommodationz.co.nz/images/faster.jpg

I’m rebuilding the wind tunnel with the wheel travelling around the outer edge of the tunnel in the hope that the cart will travel faster than the wind at a slower speed so I can video it. Will post the video if it works.

[Michael C]

Meanwhile . . . back in the workshop - I’ve built a circular wind tunnel to test if DDWFTTW is possible in a “real” wind. Unfortrunately the cart travels so fast it’s not easy to video to see what’s going on. On a TT or TM the observed speed of the cart is the speed of the cart above wind speed. In “real” wind however it’s the speed of the cart above wind speed plus the speed of the wind (quite fast). So at this stage I am only able to provide photos of the results . . .

Interesting. How are you creating the wind?

[ynot]

Interesting. How are you creating the wind?
The constant wind is being created by a large impeller at the bottom of the circular tunnel. I will provide photos of all the working pieces when I’ve finished the new design.

[semper]

Seems like the split thread has been strangled, Humber no wiser.

[John Freestone]

Ynot, I am well impressed with your have-a-go attitude, and would love to know more about how you've made your circular windtunnel. It looks a bit heath-robinson, but there's a place for that kind of engineering. I imagine that this method is quite unique in the history of DDWFTTW. The moving turntable in still air isn't, but making a windtunnel of 'infinite' length to test the cart in "real wind" ;) may be. Of course, detractors might say that it's not a real wind anyway, it's an artificial cyclone or something, and rant incoherently about friction and centrifugal force, but making a cart beat the tailwind in such a circular windtunnel is a good demonstration, combining the aspects of energy input to the air instead of the surface with easily demonstrated steady state. A knowing nod should go to the treadmill testers, who know that these aspects are not relevant to their results with a suitable understanding of mechanics, but for those with less education in the subject, the energy input at the belt, "still" air, and the need to prod the cart with a spork, tie or hold it back, or put it on a slope were recurring objections.

Something like this idea had occurred to me - I wondered about a circular pipe for my pipe-racer - but I didn't think of a suitable way to drive the air or other fluid round the pipe or trough without getting in the way of the cart. Another method I wondered about was to use a water-cart sunk in the bottom half of a circular trough, with paddles above moving the water round. That would work with air, too, and I imagine that your design must be something similar with the driven air below the turntable. I look forward to seeing more about it.

I suppose you have thought of this, but you might find that the air is directed even better by constructing upper and inner walls for the cart, although you'd have to leave a slot for the tether arm. The outer wall could be continued into a lid {ETA: some of this would need to be removable and preferably transparent}, integral with a partial inner wall coming down not quite as far as the arm. Maybe that's quite unnecessary though, and you seem to have had success with it already.

[semper]

Yeah, I guess basic physics has no place at JREF anymore. The most interesting thread has been squashed. Cmon over to; https://richarddawkins.net/forum/viewtopic.php?f=5&t=73123&p=1762501#p1762501

[fredriks]

Looked thread for 24 hours. Not much better at RDF....

I actually believe that it is more moderating on RDF compared to here in general.

[mender]

I can hardly blame the other guys for not wanting the kind of garbage that was being spouted at the last; that was supposedly a scientific arguement.

[Dan O.]

That was a shameful display. That the shame was reflected on JREF makes it worse.

Next time you visit another village, you should take some time to learn the local customs and rules before continuing your private party in their town square.

This discussion is way off topic for this thread and forum. If you want to continue it, I would suggest asking a moderator to move it to the community forum with a suitable title and introduction.

[semper]

I think that discussing ddwfttw's effects on forums and moderators is on topic. It is remarkable that such a little physics experiment can generate such vehemence, rhetoric and passion, that discussion in forums such as this can overload the capacity of moderators so quickly.

Was it the same for Galileo and Newton in their time? Such ideas meeting stubborn resistance, debate being stifled by political imperative?

[spork]

Was it the same for Galileo and Newton in their time? Such ideas meeting stubborn resistance, debate being stifled by political imperative?

From wikipedia:

"Galileo was eventually forced to recant his heliocentrism and spent the last years of his life under house arrest on orders of the Roman Inquisition."

It was one of the most shameful events in scientific history (in my opinion).

[spork]

That was a shameful display. That the shame was reflected on JREF makes it worse.

If the management of JREF is ashamed for having put one of the most active threads under moderated status, that is their shame to bear. If they are not, then no shame was reflected on JREF.

[John Freestone]

Ynot, how you getting on with that new design? I'm itching to know more about it.

[recursive prophet]

Me too, Y'not. I'd also like to know if perchance you've ever attempted to weigh the pressure of the guidance arm at point of contact on the disk, and if you've ever tried running it without the prop? Just curios.

[ynot]

Have been very busy with business and travelling lately so haven’t had any spare time to spend on the new circular wind tunnel. Hope to be able to get some time to work on it next week.

Can’t see any purpose to weighing the pressure of the guidance arm at point of contact on the disk or running the cart without a prop. Was going to run it with a flywheel in place of the prop at one stage but what I was wanting to find out has been answered by other tests.

DDWFTTW seems to have lost interest on this forum.

[recursive prophet]

Thanks for taking the time to answer, Y'not. Surprised your eyes haven't been tingling. People talkin bout you, dude. I forgot to invite you to the party cause you never really posted on the Validity of Classical Physics Thread. The debate with humber and Christoph continues, with a couple new non-believers joining the fray.

Anyway, if you get a chance I would like to know the load on the restraining arm. Your video is linked often, and the Fr has become one of issues. Also, did you ever mention minimum disk speed required, and how do you measure that?

If you get a chance you really should drop in on the new DDWFTTW (http://www.richarddawkins.net/forum/viewtopic.php?f=5&t=74988&p=1815252#p1815252) thread. It started on March 4, and is already up to 2,704 posts shattering all previous records for the forum, maybe the entire site. Pt. 3 began on March 10. Do stop by. John F, spork, Tad, mender, the whole gang are all goin srtong. And of course, we're all here..because we're not all there. :rolleyes: --rp

[ynot]

Thanks for taking the time to answer, Y'not. Surprised your eyes haven't been tingling. People talkin bout you, dude. I forgot to invite you to the party cause you never really posted on the Validity of Classical Physics Thread. The debate with humber and Christoph continues, with a couple new non-believers joining the fray.

Anyway, if you get a chance I would like to know the load on the restraining arm. Your video is linked often, and the Fr has become one of issues. Also, did you ever mention minimum disk speed required, and how do you measure that?

If you get a chance you really should drop in on the new DDWFTTW (http://www.richarddawkins.net/forum/viewtopic.php?f=5&t=74988&p=1815252#p1815252) thread. It started on March 4, and is already up to 2,704 posts shattering all previous records for the forum, maybe the entire site. Pt. 3 began on March 10. Do stop by. John F, spork, Tad, mender, the whole gang are all goin srtong. And of course, we're all here..because we're not all there. :rolleyes: --rp
So people haven’t lost interest in DDWFTTW they have just moved to another forum. Had a quick look at the “Dawkins” thread and it’s not a “party” that interests me much. I would rather see quality of posts rather than quantity. Couldn’t see where people were “talkin bout” me. Did you mean that forum/thread or some other?

Have found some time to do some work on the circular wind tunnel and things are progessing well. Thanks to John Freestone and yourself for reminding me to keep at it.

[recursive prophet]

You know, I should have linked you back a few pages on that thread Y. I just sent where we were at that moment, which was a low point. I think there's also been some interesting discussion, and other perspectives added by several RDFies new to the subject. As testing has become the major issue of late, perhaps some of it will drift back here. The question of various types of wind tunnels has also come up, so I'll pass on that you're working on one.

Have to confess that after following this topic from my_wan's OP, I am still not completely convinced the cart can perform as claimed in actual wind on the ground, though given all the converts do lean in that direction. Have you tried gearing the propeller to function as a turbine just to see what happens? And again when time permits I would like to know the arm load on the wheel.--rp

PS. Yeah, you were mentioned by name several times and many links to your video-at least a dozen-as the steady state question kept coming up. Oh, and again what speed is the wheel/disk going, and what is the minimum speed required for the prop to advance??

[Subduction Zone]

rp and others, yes the action on the Dawkin's website can get a bit vitriolic to say the least. And humber and Christoph are as full of nonsense as ever. But it does allow us to sometimes polish the arguments for DDWFTTW. For example did you see spork's analogy with the cart on the treadmill on the truck. I reprised it later and Michael C added a very nice illustration. If you have any questions about the validity of the treadmill tests this should answer them for you. No math or complex engineering knowledge needed. Even a total tyro to physics should be able to understand it. Take another look there rp, I will keep a civil "toungue" on my keyboard when I answer you.

[Michael C]

Have you tried gearing the propeller to function as a turbine just to see what happens?

Here's a prediction based on both theory and praxis: in this configuration the cart will reach a constant speed less than that of the wind. From the observer's point of view, this will mean that the cart will be seen to be going backwards on the turntable at a constant rate, in the same direction as the turntable but not as fast as the turntable.

And again when time permits I would like to know the arm load on the wheel.--rp

What do you mean? The weight that the arm adds to the wheel? Or the tension in the arm? Or something else?

I guess you are remembering humber's comments about the tether arm: something about it providing a reaction force. I have already explained why the tether arm cannot contribute to acceleration in the direction of travel. It's somewhere in the first thread on Dawkins, but I'll happily go through some details again if you have specific questions.

Oh, and again what speed is the wheel/disk going, and what is the minimum speed required for the prop to advance??

There will be a minimum wind speed for any particular DDWFTTW cart: for winds under this minimum speed the cart will not run faster than the wind. The actual minimum speed will depend on details of the cart: size of propeller, efficiency of propeller, frictional resistance in the axles... The minimum speed will not be the same for all DDWFTTW carts.

This is nothing surprising: many machines have a minimum speed necessary in order to perform a particular function. Any particular plane has its own minimum speed necessary in order to take off: move it forward at less than this speed and it'll happily roll along the ground, but it won't fly.

What I'm wondering here is: why do you want to know the minimum necessary speed for ynot's cart? Are you trying to work out what minimum speed is necessary for "real wind" trials? Since ynot's cart is quite different from spork's, or any other cart that does not need to be tethered, there's no guarantee that the minimum speeds will be the same, or even similar.

[recursive prophet]

@SZ: Thanks for the help, and you are definitely not one of the egregious offenders on RDF. You have to get really down and dirty to stand out in that crew. :D To me spork’s treadmill on a truck makes as little sense as humber sees in it. The ‘electric powered ground’ is still driving the prop instead of the reverse as it is in the wind. You still wouldn’t have the resistance you would as the prop attempted to exceed wind speed while turning the cart’s wheels on the ‘real, stationary ground.’ I just can’t grok the equivalence despite all I’ve read trying to explain it.

What I'm wondering here is: why do you want to know the minimum necessary speed for ynot's cart? Are you trying to work out what minimum speed is necessary for "real wind" trials? Since ynot's cart is quite different from spork's, or any other cart that does not need to be tethered, there's no guarantee that the minimum speeds will be the same, or even similar.
Michael: I remember your explanation of y’not’s wheel, but what I still fail to grok is how you can be so certain the wheels turning the prop will be the same as the prop driving the wheels. I asked about this last night on RDF but my questions got lost in the ‘pleasantry exchanges.’

I believe the addition of the tether arm solves one problem while creating another. I would still like to know how much tension it adds and what the weight is of the prop and wheel on the disk. You have argued about the difference between a tethered balloon and an un-tethered one in the wind, yet here claim the tether makes no difference. Personally I still think we should forget balloons, boats, and treadmills and focus on carts on the ground in the wind. I realize such tests come with their own set of problems, but hopefully you will agree little has been tried to date beyond Goodman’s very simple and IMV unscientific experiment.

[Michael C]

Michael: I remember your explanation of y’not’s wheel, but what I still fail to grok is how you can be so certain the wheels turning the prop will be the same as the prop driving the wheels. I asked about this last night on RDF but my questions got lost in the ‘pleasantry exchanges.’

I'm not sure what you mean here. The prop is always being turned by the wheels.

I believe the addition of the tether arm solves one problem while creating another. I would still like to know how much tension it adds and what the weight is of the prop and wheel on the disk. You have argued about the difference between a tethered balloon and an un-tethered one in the wind, yet here claim the tether makes no difference.

The difference is the direction is which the tether is pulling. In the case of the tethered balloon, the tether can exert a force against the direction of movement of the balloon. In the case of ynot's cart, the tether is always acting at right angles to the direction of movement.

A force at right angles to the direction of movement does not produce an acceleration in the direction of movement.

All the tether does here is to constrain the movement to be circular. It doesn't matter how much tension is present in the tether arm, this tension cannot accelerate the circular movement.

[Subduction Zone]

rp, the point about putting the treadmill on the truck outside is to show you that the surface of the treadmill inside is exactly like the ground outside. The top of the treadmill on the truck is stationary with respect to the ground. So the wind blowing over it is not due to the treadmills motion, as it is with the inside treadmill, the wind blowing over it is the "real wind". I hope you can see that.

[recursive prophet]

I'm not sure what you mean here. The prop is always being turned by the wheels.
Lets stop right here. I've seen this stated before and still don't understand the claim. I can see how the wheels turn the cart on the belt, but unlike the belt the ground isn't moving in reference to the wheels of the cart. It is stationary, so how can it be the wheels turning the prop? I thought the wind was doing that, and the prop then turned the wheels when on the ground. Glad this came up as it is a major factor in my lack of understanding. Please explain.

[ThinAirDesigns]

Lets stop right here. I've seen this stated before and still don't understand the claim. I can see how the wheels turn the cart on the belt, but unlike the belt the ground isn't moving in reference to the wheels of the cart. It is stationary, so how can it be the wheels turning the prop?

A: When the cart is on the treadmill set at 10mph and the cart is sitting still relative to the room, the wheels are moving relative to the rolling surface at 10mph. You would probably agree that if you put a speedometer driven off of those wheels you would see 10mph on the speedometer.

B: When the cart is on the ground and is moving downwind at 10mph, the wheels are moving relative to the ground at 10mph. You would probably agree that if you put a speedometer driven off of those wheels you would see 10mph on the speedometer.

I simply can't comprehend what you can possibly mean by "...unlike the belt the ground isn't moving in reference to the wheels of the cart. It is stationary, ..."

In both cases, the wheels are moving the same speed across the rolling surface.

I thought the wind was doing that, and the prop then turned the wheels when on the ground.

You need to stop thinking that -- even if you don't understand *how* it can be, I promise you it does you no good whatsoever to continue to attempt to grok it the other way.

JB

[John Freestone]

Lets stop right here. I've seen this stated before and still don't understand the claim. I can see how the wheels turn the cart on the belt, but unlike the belt the ground isn't moving in reference to the wheels of the cart. It is stationary, so how can it be the wheels turning the prop? I thought the wind was doing that, and the prop then turned the wheels when on the ground. Glad this came up as it is a major factor in my lack of understanding. Please explain.
Hello RP. Are you sitting comfortably? :D

The prop blades are set at such an angle that they aren't allowed to act as turbine blades. As you can see in the last (cart) video of spork's, when lifted off the ground, the tailwind blows the prop round as a turbine, but when put on the ground (in this case he uses the treadmill turned off) it switches direction. Now, why is that? What does it mean? Well, in the first instance there is virtually no load on the prop-turbine (i.e. there is nothing stopping the rest of the machine and the wheels turning in any direction the prop-turbine is tending to turn them. It's worth pointing out, of course, that the prop-turbine (or "spinny thing" (ST) as I've been calling it there) isn't actually one or the other. The same gizmo can be used as either. Ok, so we've got our first bit of information: nothing stopping the wheels go in either direction, and the wind does what wind would do to a "windmill" - a turbine generating electricity, for instance.

Next thing to note is that, if you were to look at the wheels during that turbining motion, while they're off the ground, they would be turning backwards. If you got hold of the wheels and turned them backwards, the spinny thing would go in the turbine direction. If you turned the wheels forward - by which I obviously mean the direction they would turn in if the cart was going forwards on them! - the ST turns as a prop.

So why does it turn as a prop when you put it down and blow wind at it from the rear? Well, because the whole vehicle is getting blown along. Do you see? If there was just a flat disk there instead, or the blades were turned to point in the "across the road" direction (part of a disk), this being called having a pitch of zero, then it's spinning wouldn't make any difference at all. If it were removed - just a cart on some wheels - it would still be blown along the ground, like a shopping cart can be seen to do in a carpark, even though it would take a little more wind power to shift it.

In the normal configuration, there is a force just like that (despite the fact that most of the wind resistance on a well-designed cart comes from the prop itself, and ALSO DESPITE the fact that the ST would, given free rein, like to turn the turbine way). So, what actually happens is that the whole cart is pushed along the road, and that overcomes the tendency of the blades to be turned as a turbine, making it act like a prop.

Think of just a wind turbine, like one of those massive ones generating electricity. Imagine it in your mind's eye, how the wind passes the blades, and because of the angle of the blades - see that angle - the air pushes each blade round in a particular direction - just one way because of that sloping angle of the blade. Now, imagine if someone got hold of the gears inside and pushed it round the "wrong" way. It's a hell of a battle - the wind's trying to turn a turbine, and we're forcing the poor thing to do the opposite. It's like that, only that "wrong-way" force is coming from the fact that the whole cart is being pushed along the ground, and that is - THE GROUND IS - turning the wheels.

Now, check that capitals bit out. If instead of having wind blowing the cart along, you keep the air still, you can get exactly the same effect by moving the ground backwards instead - the cart doesn't feel any different forces. Now to our biased human minds, these things look very different indeed, but really they are no different except in the details outside of that motion. The cart doesn't touch anything except the surface it's on and the air its in. Does that help? That's the stupid thing about humber's and C's endless rant about the belt pushing the wheels, driving the wheels. If they got their heads round the above, they'd see that the cart is pushed along the road and the road drives the wheels, just the same (in all relevant details).

Going back to where I started, if you've understood that, it is the pitch chosen for the prop blades that makes that possible. There's a lot of detail about that elsewhere, but basically it's kept fairly shallow (across-the-road, a short pitch) - if the slope was made gradually steeper, the blades turning more towards the down-the-road direction, it will get to a point where the blunt pushing force - the trolley-dash force - of the wind got too weak to overcome the turbine tendency. The turbining would win the battle, and, because there's no alternative, the wheels would turn backwards, and the cart would actually back up into the wind (actually, for me, that was much easier to see than DDWFTTW).

I know you've also puzzled about how, at windspeed, there can be any puff left in the wind. I don't know if you've got that bit yet, but let me know if you'd like me to have a go at that part as well.

ynot - no pressure, I was just curious. I guess I can relax and know that if you got round to it you'd post, so I needn't keep asking.

[John Freestone]

I simply can't comprehend what you can possibly mean by "...unlike the belt the ground isn't moving in reference to the wheels of the cart. It is stationary, ..."

In both cases, the wheels are moving the same speed across the rolling surface.
JB, I think it's just that simple human bias we mortals have - some, like humber, can never get over it, or if they do, they pretend never to have done so. RP is less susceptible, I hope, but makes that mistake here.

RP, I think when you go back to the road situation in your mind's eye, you remember the motionless (balanced) cart on the treadmill, "put it" on the road, still motionless, and that gives no relative velocity between road and wheels. But that situation of "still" for the road-cart is when it's stopped - the wind is whistling past it from behind, and the brake's on. We're waiting to get going when the wheels aren't moving!

You have to remember that the treadmill only demonstrates windspeed and near windspeed, and transfer that same situation back if you're going to compare it with the road. So the treadmill models the road cart whizzing along at windspeed.

[ThinAirDesigns]

JB, I think it's just that simple human bias we mortals have - some, like humber, can never get over it, or if they do, they pretend never to have done so. RP is less susceptible, I hope, but makes that mistake here.

I guess so, but it's really freaky -- if RCP were driving his car next to the cart as it went down the street he could look at his own car's speedometer and clearly see that is says "10mph" (or kph). I just don't get here his statement comes from that on the street the cart's wheels are stationary.

JB

[John Freestone]

I guess so, but it's really freaky -- if RCP were driving his car next to the cart as it went down the street he could look at his own car's speedometer and clearly see that is says "10mph" (or kph). I just don't get here his statement comes from that on the street the cart's wheels are stationary.

JB
Hey, we're starting a psych-RP thread! Sorry, RP. Maybe you'll take it as a compliment. Reading the whole piece of text and what came before, it looks like this is part of his confusion about how on earth the cart gets going at all on the road, because the ground isn't powering it, and he's been persuaded by those pesky persuaders that if it's driven by the wind instead, that can only be done if it's turbining. I think that my long post earlier might bridge that gap if we don't distract him from it too much.

What amazes me is how many times the content of that must have been written on these threads, and that I wrote two long posts explaining that to C only last week or thereabouts - one with a diagram of a mechanical screw instead of the prop, IIRC. So I'll not hold my breath. However, the noise to signal ratio around here could mean people like RP aren't entirely to blame if they miss something central.

You know, what you, spork et al really need is a central place, er website they call 'em, where all of the correct physics and explanations and the most relevant analogues can be collected - instead of this mess of forums - or is there such a place and I've missed it? Then newbies can just be given one link and it could save an awful lot of bother. I did complain myself in the earlier thread that I was having to ask questions and get answers and and raise my internal mental objections to the bits of explanation I was getting (which was sometimes seen as more critical than it was meant), in amongst a raging argument, but nobody was explaining what the answer was clearly, top down, this is how it works.... That, as I observered, was ok, because it was meant to be a brainteaser. But this has been going on a long time now. We've had the reveal moment. People need a clearer explanation that's always readily available. This repetition and drip feeding is a problem now, IMO.

[ThinAirDesigns]

You know, what you, spork et al really need is a central place, er website they call 'em, where all of the correct physics and explanations and the most relevant analogues can be collected - instead of this mess of forums - or is there such a place and I've missed it?

http://dwfttw.blogspot.com/

JB

[mender]

RP, if you don't mind I'll try out another way of explaining how the cart works to you. I feel that this thread might be a better place to do that. I'd like to go through this without humber or Christoph butting it if possible. Once we get through this, I may try it on them if they'll cooperate. I feel that you may have some of the same blind spots as them but you definitely are much more relaxed about that! From the questions you're asking now, I'd say you're ready for the chewy parts!

Most of this will be idealized, i.e., no losses or slippage unless specified. Also, we'll ignore any influence by the wind on the body of the cart and say that only the prop feels the wind. We'll adjust that later.

Let's have humber and his bike participate in this example since he wants a test on this. Let's build a cart with a variable speed transmission and a clutch between the wheels and the prop for the test. The wind will be a nice steady 12 ft/second tailwind.

First, set the cart in the wind with the transmission in neutral, with the cart not moving and allowing the prop to spin freely. What speed does the prop turn at? That depends on two things: the speed of the air going by, and the pitch of the prop. The air is going by at 12 ft per second as verified by the on-board anemometer, and the prop has a pitch of 8 inches per revolution. That means that the prop will spin freely at 18 times per second or 1080 rpm.

An important thing to remember is that if the propeller is turning at this freewheeling speed, it is neither taking energy out of nor putting energy into the air as it moves by. Slowing down the prop from that speed will take energy from the air (cart speeds up). Speeding up the prop above the freewheeling speed take away energy from the cart (cart slows down). More on that later.

Back to our cart, sitting on the ground with the 12 ft/sec wind blowing on it. The prop is spinning at 1080 rpm. Humber hooks up a tether to his bike and starts pedaling downwind.

As humber gets to 3 ft/second, let's freeze the picture for a moment. The cart is moving at 3 ft/sec. Let's say that the wheels turn once per foot,which gives us a wheel rpm of 3 x 60 or 180. The on-board anemometer says that the air is going at 9 ft/sec., which means that the freewheeling speed of the prop is now only 810 rpm. You decide to see what the gear ratio would need to be if you engaged the transmission. Easy enough: 180/810 is .22:1.

Now we unfreeze and let humber get up to 6 ft/sec and repeat. Now the relative air speed is only 6 ft/sec, the prop's freewheeling speed is 540 and the wheels are turning at 360 rpm. The gear ratio needed to keep everything turning at the same rpm is 360/540 or .66:1.

Next speed is 9 ft/sec. The relative air speed is verified by the on-board anemometer as being 3 ft/sec, the prop only turns 270 rpm and the wheels are turning at 540 rpm. Now we see a big jump in the gear ratio needed to engage the transmission without issues, or 2:1. The next step is even bigger.

Okay, now humber is riding at 12 ft/second or wind speed, the relative airspeed is 0 ft/sec so the prop stops turning, and the wheels are turning at 720 rpm. Now what is the gear ratio needed? Well, the ratio is infinite but don't dwell too much on that at the moment, the important part is that the prop is stopped.

Just to be thorough, humber decides to pedal faster and gets to 15 ft/sec. Now the prop is turning again but the other way! Not a big surprise but an important point. The rpm of the prop is again 270 rpm but the other way, and the wheels are turning at 900 rpm. The gear ratio is 3.33, on its way back down from infinity but on the other side - we'll call this the positive side since we have to go faster than the wind to need this ratio. That of course would make the other side negative, since that side only applies to below wind speed.

Humber is a wild man, now he gets to 18 ft/second! The prop is turning faster because it now sees a relative air speed of 6 ft/sec with an rpm 540 rpm in the plus direction. The wheels are turning at 1080 rpm, so the gear ratio needs to be 2:1. This trend of gear ratios continues downward as the cart goes faster and faster. The exact ratio is not that important now but we'll need that if we get into advance ratios.

RP, I hope the concept came through, that the prop has a speed and direction that it wants to turn depending on how fast the cart is moving along the ground in a steady tailwind. Below wind speed, the prop wants to turn one way and the gear ratio has to be negative; above wind speed it wants to turn the other so the gear ratio has to be positive. That's what spork's second last video showed, the difference between a slower than wind cart and a faster than wind cart.

At this point, we aren't taking any energy out of the wind, just going along with the wind speed, Humber is doing all the work for us! All we're after is the way the prop has to turn when the cart is below, at, and above wind speed. Christoph acknowledges this by saying that the cart's gearing can't suddenly change the direction of prop rotation when the cart goes faster than wind speed. We'll get into the power part after you have this done pat.

I hope that was clear. Please ask about any stage that isn't and we'll start there. Also, please let me know if this helped at all or was just confusing. No pressure!

P.S. Sorry for the long post!

[recursive prophet]

Mender: Thanks so much for the thoughtful reply. It does remind me a bit of Maxwell’s Demon with your infinitely geared transmission. For as humber and Chris point out, why wouldn’t the turbine act as a brake at 15fps? It would be pushing against the direction the cart is moving. So please do jump ahead, and to cover the point Chris makes about the sudden change in rotation, and how it couldn't overcome the resistance of the wind from the opposite direction once wind speed is exceeded?

Sorry if I’m still missing the point. I just can’t help but wonder how relevant the example is to an actual cart, which only has one gear. As an aside, did you catch the article in the March Popular Mechanics on the prop car races in Stuttgart? They do have a lot of gears, and a prop that swivels, yet there was no mention of going downwind faster than the wind. I recall the winning car averaged about 15mph in the race. A lot of tacking going on I’m sure.

TAD and John: Sorry I missed your replies when I responded to mender earlier. Think you screw example was the best yet, JB, in helping me grok what's happening. Anyway, thanks for the online 'intervention,' and good job on the blogsite JB. For just a modest monthly payment of $100 I won't tell humber about it. :lol:

[ThinAirDesigns]

As an aside, did you catch the article in the March Popular Mechanics on the prop car races in Stuttgart? They do have a lot of gears, and a prop that swivels, yet there was no mention of going downwind faster than the wind. I recall the winning car averaged about 15mph in the race. A lot of tacking going on I’m sure.


No tacking at all.

http://www.nextenergynews.com/news08/next-energy-news8.29.08b.html

In this first time ever race the participating teams were challenged to drive directly into the wind, without tacking. During the preliminary races, the Stuttgart Ventomobile had already proven to be the most lightweight and most efficient vehicle among the contestants when, with its 130 kg, it succeeded in racing at 64% of the wind speed directly against the wind. From then on it was considered a serious contender for the win

There's no mention of downwind because it was an upwind race. Believe it or not, there are still people who believe its impossible to build a wind powered vehicle that can drive directly *into* the wind. We ran into a physics professor who wrote that *exact* thing -- all the while these kids in Europe are RACING directly into the wind.

Goes to show the state of our traditional education system here in the states.

JB

[RossFW]

Tad, do you think those vehicles would also work DDW? Perhaps we sholud contact the organisers of the event and suggest that next year, the event be either DDW, or best agregate time in BOTH directions.

[spork]

Michael: I remember your explanation of y’not’s wheel, but what I still fail to grok is how you can be so certain the wheels turning the prop will be the same as the prop driving the wheels.

I know you really like to ask that question. But the answer will always be the same. The wheels always drive the prop. It's never the other way around for a DDWFTTW cart. That's the thing about science - you always get the same answer because it's based on fact.

Lets stop right here. I've seen this stated before

Yup. And next time you ask, you'll see it stated again.

Here's a better way to look at it... the treadmill IS a road.


The question is:
- How long would that treadmill have to be before you thought it was a road? 1 mile, 100 miles, 1000 miles?
- How wide would it have to be? 20 miles?
- Would there have to be houses and trees on it?

If you were standing on an asphalt surface lined on both sides with houses and trees - cars coming and going. You can see all the way to the horizon in every direction - what would you do to figure out whether you were standing in the road, or standing on a very big treadmill?

Really, answer that - OR please don't ask again.

[spork]

Tad, do you think those vehicles would also work DDW? Perhaps we sholud contact the organisers of the event and suggest that next year, the event be either DDW, or best agregate time in BOTH directions.


To go downwind they simply need to change the gearing so the advance ratio (prop advance / wheel advance) is less than one. For upwind it's exactly the opposite.

There is a region of "overlap". You can operate a downwind cart with the prop acting as a turbine, but it will never reach windspeed. This case is interesting only as it pertains to harvesting energy from the wind, and even then, it's a footnote.

[recursive prophet]

IHere's a better way to look at it... the treadmill IS a road.

If you were standing on an asphalt surface lined on both sides with houses and trees - cars coming and going. You can see all the way to the horizon in every direction - what would you do to figure out whether you were standing in the road, or standing on a very big treadmill?

Really, answer that - OR please don't ask again.
I would suck my finger and stick it in the air to see if I could detect wind. If I couldn't, I'd assume I wasn't moving. HOW CAN THE ROAD BE THE FORCE THAT TURNS THE WHEELS WHEN UNLIKE THE BELT IT DOESN'T MOVE!!!???

[Subduction Zone]

I would suck my finger and stick it in the air to see if I could detect wind. If I couldn't, I'd assume I wasn't moving. HOW CAN THE ROAD BE THE FORCE THAT TURNS THE WHEELS WHEN UNLIKE THE BELT IT DOESN'T MOVE!!!???

Don't think of it as the road (treadmill) that gives power to the cart. It is the difference in speed between the wind and the road that powers the cart. This way it does not matter if the wind is moving and the road is still (outside situation) or if the wind is not moving and the road is in motion (inside, treadmill situation). I am sure that even with the still wind you could reach down and feel the road zooming by underneath you.

[RossFW]

rc,

would suck my finger and stick it in the air to see if I could detect wind. If I couldn't, I'd assume I wasn't moving.

Really? How would you know you wern't just moving at the speed of the wind? If you DID feel something, how would you know it was you in motion, and not the air in the form of wind.

I'm afraid you are falling inti humber territory here.

What is your definition of "Moving". Motion is relative. When talking about moving, you have to specify "Relative to what". As has been poited out many times, sitting in front of your computer you are attached to a planet that is rotataing, orbiting and is in a galaxy that is receding. So is a road. So do you want to stick to your statement that "The road doesn't move.

EVERYTING moves from the poit of view of an observer moving at a differnet velocity to it. EVERYTHING is still from the POV of an obserever moving at the same velocity as it. Everything is SIMULTAINIOUSLY still AND in motion WRT different observers.

In order to find data to use in physical equations, we can't say "That is moving, that isn't". We HAVE to specify the RELATIVE motion between things. This was Humbers and Christophs big hang up with the balloon. They were convinced that wind is "Movement" without being able to come to grips that it is only movement RELATIVE to the earth, and that if the earth was taken out of the calculation, the relatioship between the balloon and the air around it was identical whether the air was "Wind" or "Still"

And so to the cart-

You say the road is still. If I am in my land yacht, sailing downwind, I look down and LO! I see the ground moving beneath me!! That is JUST as valid a statement as saying I'm moving along the road. The fact his, the road and I have a RELATIVE velocity.

The cart works because of the RELATIVE velocity of a surface and the air. If you can hold up an anomometer (or a wet finger!!) and detect movement, that is EXACTLEY the same physical state whether you are moving throug the air, or it is moving past you.

In one instance, the power to provide this relative motion comes from a motor- in anothe the differential pressure between air systems. eitherway, hold up your finger and it gets cold, UNTIL you travel at the same speed as the air around you.

[sol invictus]

I would suck my finger and stick it in the air to see if I could detect wind. If I couldn't, I'd assume I wasn't moving. HOW CAN THE ROAD BE THE FORCE THAT TURNS THE WHEELS WHEN UNLIKE THE BELT IT DOESN'T MOVE!!!???

If that's your definition of "not moving", then unless it's an extremely still day the road is moving.

RP, just FYI - I read most of the posts in the threads here, and occasionally I drop in and read some of them over at Dawkin's forum. I happen to know a fair amount of physics (you can read some of my posts on this forum and judge for yourself). Humber and Christoph are completely and totally wrong, and I've rarely if ever seen any of the other regulars say anything incorrect. Their biggest failing is not catching some of humber's mistakes, but there are so many it's hardly surprising (although there was one pretty egregious one, something about torque and angular momentum where he had the wrong equation - 1/r instead of r, IIRC - and used it many times with no one noticing).

I actually share your view that humber is pretty smart. And I'm impressed that he manages to be wrong in nearly every single statement about physics. My conclusion is that he is doing so intentionally - that he's some kind of uber-troll that keeps things going like that. I was more or less joking about him being spork's sockpuppet (although I wouldn't totally exclude the possibility).

[ThinAirDesigns]

(Recursive Prophet from Dawkins):
I know what 'inertial frames of reference' are;
-
RCP,we *know* the above statemen't ISN'T true, even a little bit. How do we know this? -- because of what you write below:
-

(again from Dawkins)
... you guys are making it a privileged frame wrt the cart.
-

HOW CAN THE ROAD BE THE FORCE THAT TURNS THE WHEELS WHEN UNLIKE THE BELT IT DOESN'T MOVE!!!???
-
RCP, your "I know what inertial frames of reference are" statement, and those following writings are MUTUALLY EXCLUSIVE.

You have no hope whatsoever understanding street/treadmill comparison until you look at yourself and say "I thought I understood inertial frames of reference, but as it turns out not only do I *not* know, the understanding I thought I had was totally wrong".

Best wishes with that.

JB

[Michael C]

I would suck my finger and stick it in the air to see if I could detect wind. If I couldn't, I'd assume I wasn't moving. HOW CAN THE ROAD BE THE FORCE THAT TURNS THE WHEELS WHEN UNLIKE THE BELT IT DOESN'T MOVE!!!???

Motion is relative. "The motion of the belt" alone can't turn anything: what turns the wheels is the motion of the belt relative to something else.

- If a hand is holding the cart against the belt, then the wheels are being turned by the motion of the belt relative to the hand.
- If there is no hand holding the cart on the belt, the wheels are being turned by the motion of the belt relative to the air, which is the same thing as the motion of the air relative to the belt.
- On the road, the wheels are turned by the motion of the air relative to the ground, which is the same thing as the motion of the ground relative to the air.

Have a look at the excellent NASA series on aerodynamics, in particular these two pages on relative velocity:

http://www.grc.nasa.gov/WWW/K-12/airplane/move.html
http://www.grc.nasa.gov/WWW/K-12/airplane/move2.html

The relationship between airspeed, wind speed, and ground speed explains why wind tunnel testing is possible and how kites fly.

In the wind tunnel, the ground speed is zero because the model is fixed to the walls of the tunnel. The airspeed is then the negative of the wind speed that is generated in the tunnel. Whether the object moves through the air, or the air moves over the object, the forces are the same.

I put that last phrase in bold type: therein lies the essential point. You can see it being made again here, with respect to flying a kite:

http://www.grc.nasa.gov/WWW/K-12/airplane/kitefly.html

It does not matter whether the air blows over the kite, or the kite is pulled through the air; the important factor for generating lift is the relative velocity between the air and the kite.

[ThinAirDesigns]

Michael, your good work in finding those absolutely perfect quotes is noted, but NASA is likely not a good enough source for RCP as they are known to get emotional from time to time. In RCP's world, Humber "pwns' NASA because of this.

JB

[John Freestone]

Tad, do you think those vehicles would also work DDW? Perhaps we sholud contact the organisers of the event and suggest that next year, the event be either DDW, or best agregate time in BOTH directions.
That's a brilliant idea. Even better - and I expect it's only a matter of time before they do this regularly - they could race on a circuit, harvesting wind energy as best they can from side, behind or in front, which would make for a very skilled sport indeed, shifting the gear ratio, pitch and propsail (is that the right general term for a prop/turbine/ spinny thing?). They'd be going about half windspeed against it and who knows, 2 or 3 times it downwind? Of course, it does suffer on the event side of things, as all such sports do - arranging the event for a windy day some weeks ahead and selling tickets!

[ThinAirDesigns]

Tad, do you think those vehicles would also work DDW? Perhaps we sholud contact the organisers of the event and suggest that next year, the event be either DDW, or best agregate time in BOTH directions.

Even as they are setup they will go DDW -- though as a turbine powered vehicle and not as fast as the wind. Since their goal was upwind, I would doubt that their transmissions are set up to vary the advance ratio, but I have no personal knowledge of their machines.

JB

[spork]

I would suck my finger and stick it in the air to see if I could detect wind. If I couldn't, I'd assume I wasn't moving.

Whether you were standing in the street feeling a breeze or standing on a big treadmill with houses and trees, you'd feel EXACTLY the same thing on your sloppy finger. In fact there is NO experiment you could to do tell the difference. You know why? There IS NO DIFFERENCE.

HOW CAN THE ROAD BE THE FORCE THAT TURNS THE WHEELS WHEN UNLIKE THE BELT IT DOESN'T MOVE!!!???

You are not equipped to understand.

[spork]

Even as they are setup they will go DDW -- though as a turbine powered vehicle. Since their goal was upwind, I would doubt that their transmissions are set up to vary the advance ratio, but I have no personal knowledge of their machines.

JB

I'm guessing they can't go DDW. I think you'd have to reverse the gear ratio (same ratio, different sign).

[ThinAirDesigns]

I'm guessing they can't go DDW. I think you'd have to reverse the gear ratio (same ratio, different sign).

That top pylon spins 360 -- which reversed the sign at 180.

JB

[John Freestone]

I would suck my finger and stick it in the air to see if I could detect wind. If I couldn't, I'd assume I wasn't moving. HOW CAN THE ROAD BE THE FORCE THAT TURNS THE WHEELS WHEN UNLIKE THE BELT IT DOESN'T MOVE!!!???
RP, I'm trying not to react to this with anger, because I've addressed that in the post above, and now someone else is addressing it, and you don't actually seem to read and think about answers, because people have addressed this several times before me and you seem not to have read those answers either.

Let me see, I'm going to stick a wet finger in the air now to work out if I'm moving. Nope. I'm perfectly still. The Earth is the centre of the universe and the sun and moon must be orbiting. Sorry about the last thousand years of astronomy, but there you have it. The wet finger proves it.

RP, when you're outside on a perfectly still day, what does that mean. If you're where I think you are, the earth is spinning at roughly 500 miles per hour there. Are you motionless? No. Is the air motionless? No. Isn't that just like spork's very large treadmill belt, with trees and hills and lakes on it, and isn't it a "still day" by the fact that the air just happens to be travelling at the same speed round the surface of the planet where you are?

If the air was still w.r.t. the centre of the planet, you would be experiencing a windspeed of 500 mph. And that's before we factor in all the motions of the galaxy, etc. In the end, as has been said endlessly, MOTION IS RELATIVE - always, to something else. That "something else" can be thought of as a place, such that your velocity is the change of distance from that point, but - because velocities are all relative - we don't know the velocity of that point either. Its velocity is also relative to somewhere else. So in effect, velocities are relative to other velocities. When you say the air isn't moving outside, you're taking that bit of the earth where you are as "zero velocity" or "your frame of reference". But if you could literally capture that velocity somehow - measure the speed of a balloon with GPS equipment onboard, etc. - and then move a little way north or south, the earth there would be moving at a different velocity, so that same "still air" velocity would now not be zero, but a light breeze.

This is the problem humber is stuck with, and actually seeing you struggle with this does make me wonder if he's never really been pretending at all, but that maybe some people are just incapable of making this mental shift between frames of reference. Even so, he adds to the problem by never believing that other people can, despite their maths actually adding up and his coming out as nonsense. You're obviously a bit exasperated with this sometimes, but you're not arsey about it.

Hi sol, I've missed you! Uber-troll, yes, probably a better explanation - he might not see how wrong he is, but he can't not see a ruddy good chunk of how wrong he is.

Hmmm, it's already weird being back here and having to watch my "ruddy" language. It's like my granddaughter has come to play. JREF is a bit like Telly Tubbies Land. Thanks for the Dawkins intro, RP. Now ruddy get this frames of reference stuff or I'm going to track you down and kick your behind.:D

But even without that - look at your question above again - I answered it with a different point. The road drives the wheels anyway if you follow the logic - the cart as a whole is blown down the road and that forces the wheels to turn. If a shopping trolley was blown across a carpark, it would make the wheels turn, wouldn't it? You wouldn't be scratching your head wondering how that's happening without a "turbine"!

[spork]

RP...If a shopping trolley was blown across a carpark, it would make the wheels turn, wouldn't it? You wouldn't be scratching your head wondering how that's happening without a "turbine"!

Of course he would. And he'd keep asking us until he got the wrong answer that fit his notion of how the world works.

@sol: there's no doubt humber got many many things horribly wrong without being corrected. Most of us simply skip any post from him more than 2 sentences long. There's only so much you can take.

[John Freestone]

Forgot to say, thanks for that link to DDWFTTW Central, JB. I'll have a better read of it when I stop laughing at C's magical frames of reference. I pick my coffee mug up off the table's frame of reference, and bring it to my mouth's frame of reference, trying not to drop it on the floor's frame of reference...

ETA: Whose site is that, BTW?

[ThinAirDesigns]

ETA: Whose site is that, BTW?

A guy by the handle of "AirShowFan" who initially saw the video when all the BoingBoing chaos hit.

JB

[John Freestone]

So is he pretty clued up on it, this AirShowFan? I mean, I know it's not YOUR cart or spork's, but I see you two, perhaps along with a bunch of others like mender, as knowing this beast inside out now. Obviously that opinion is based on only understanding part of it myself, but also on seeing you answer questions confidently (that make sense), predict, test, fess up when you make a mistake, and put endless effort into educating people on all sorts of sites. I guess spork must now be more than anyone the DDW cart champion in terms of conversations (though obviously your less frequent posts are much more important ;)). I trust you guys, and feel that you ought to have a site. Not that I'm telling you what to do, and you're doing a lot already. It should just have a "JB/Spork Approved" logo.

Of course, ASF could be TAD, but if I thought such a thing, I'd keep it to myself. I see spork has posted there under 'Anonymous', which is a really great way to hide your identity. :D

[spork]

So is he pretty clued up on it?

I recall AirShowFan on at least one of the blogs. My recollection is that he had a pretty firm grasp on it. I vaguely recall a few things I would have changed, but I don't think anything major. I'll go back and give it a read.

I see spork has posted there under 'Anonymous', which is a really great way to hide your identity. :D

I've never intentionally posted as anonymous, but there are a couple of blogs that let you post without logging in - so I have some posts without my signature.

[John Freestone]

Yeah I know. I was juss funnin yer.

[recursive prophet]

First sol: Miss your insights and laconic humor. And yes, I’m aware of your standing in the physics community here, and even mentioned it when I was posting your replies on the thread the mods split into a topic here over to that evo thread on rdf. Glad to see you still think its possible spork created humber as the perfect strawman for getting his message across. Like you I doubt it though. If he even HAS any day job it’s hard to imagine he’d have the time, given all his other activity in cyberspace. Either way I certainly find the back and forth quite entertaining, and do wish you and Dan O and Fredrik would join in.

Many thanks for the time you’ve all spent-John, mender, Michael, Ross, spork, and even you JB, who are likely the most annoyed by my ‘willful ignorance.’ Perhaps never before in history have so many extremely bright people made such a stellar effort to pour understanding into such a small brain. I know, you’d all claim I’m a distant second to humber, but as you know I disagree and still see him as being brilliant whatever his game or mistakes he’s made. Just the fact sol-arguably one of the brightest bulbs in a marquee that would stand out in Vegas-thinks he might possibly be a creation of spork’s manly hands tells me humber is no idiot.

I will keep an eye out for posts here, but from now on will reply only on rdf. When the TVOCP thread was put on moderated status, I made the mistake of taking on the mods here in the management forum. I just receive my second formal warning today for being Off Topic, and again threatened with suspension. My last 4 replies to TVOCP never made it, though the last was a short reply to Dan and totally on topic. I would like to see this thread revitalized and continue, and fear my name coming up on the main menu will draw unwanted attention. I even considered PMing this message. So I’ll see you on the Dawk side, and hopefully will win my appeal and feel it’s safe to come back here soon. Not surprising I ran into trouble, eh? You guys all know what an arrogant, aggressive, self-glorifying troll I am. Only here did they find me out.

Sincere thanks again. You’d likely be amazed at the high regard I have for all of you. So why haven’t I drunk the cool aid? Cause I’ve chugged it before, and found that even a very impressive consensus can be proven wrong. I sip now, and wait to see what can be scaled and measured. Even questionable, preliminary testing can be quite informative. Old school, chaps. Don’t often grok the equivalency models you geniuses come up with, and one of many questions I asked that got lost in the noise was how Newton’s Cradle-which humber mentioned way back-wasn’t relevant to this discussion wrt the ke. Believe mender replied, but I recall more questions ‘razed’ and I never followed up.

Back to more thoughts and GS searches on frames of reference. I had seen those 4 NASA links you posted in an earlier search Mike-but thanks. To be honest found them hard to get my mind around. I mean on many levels were literally talking rocket science here! Is there an Idiots Guide? I read “Relativity for the Million” years ago. Did you guys catch the double entendre of humber’s Walmart frames, by the bye? This whole discussion has enriched my life immensely. Kudos to all. --Arpie

[ThinAirDesigns]

Well, well. With a tiny bit of digging, we find RCP being accused by JREF moderators of troll-like behavior.

I just can't fathom such a thing. :rolleyes::rolleyes:

JB

[RossFW]

RP,

You are obviously such a nice guy at heart, it's a shame some of your writing comes across as caustic.

Then again, I guess the problem is that to most of us, Humber and Christophs errors are so "Deer in the headlights" obviously wrong, that we will immediately tend to interpret posts not realizing this as hostile, whilst that is not your intent.

I agree that Humber has something going on, if not just a skin as thick as a Rhino. That he can continue to argue against a whole bunch (and if you totted it up, with those that have come and gone, you'd be talking something like 25-2) and not even once look like he's considering that he is wrong in even one area, when he has frequently been caught out and shown the inarguable evidence, certainly takes stones of boulder-like proportions.

Perhaps, though, if I can acquaint you with some of his most egregious ideas, you will get a taste of why his continued obstinance gets up our noses so.

Physics is like a house. It needs foundations. Without them, any further building just falls down flat.

Humber's foundations are made of play-doh!

For instance, Newton is taken as the Father of modern Physics. His laws of motion, formulated 400 years ago, sent men to the moon and spacecraft at Neptune. They are simple, elegant and an understanding of them is essential to understanding anything else in the realm of physics.

Newtons first law establishes two golden principles.

Humber dis-agrees with both of them.

Firstly, the fact that a body keeps a constant velocity UNLESS acted on by a force (direct Humber quote- "You suggest motion without force!" ).

Secondly, that there is no privileged frame of reference, and that motion is relative (NUMEROUS refutations- the latest to your "Fly in plane" scenario- "The fly is traveling at 1m/s, no other interpretation is necessary").

What we've weaseled out of Humber over time is that he was raised in a remote community, has a diagnosed learning disability, and, while trade-qualified, seems to have no real formal education. The fact that he missed out on the very basic fundamentals of Physics, then went on and self-taught himself a great deal, but from an incorrect starting place, has lead to this rather unique individual who has a great deal of knowledge-all of it wrong!

A big difference between our fields and yours is that there IS absolute truth in the physical world. There are no grey areas. You may admire Humber for his skills in the Psychological world, but we just can't, because he isn't "Good" or "bad" or "better". You are either right or wrong, and he is amazingly consistent at being the latter.

[John Freestone]

Well said, Ross. You made me feel quite sorry for humber there for a moment. That summary is brilliant: "this rather unique individual who has a great deal of knowledge-all of it wrong!"

What I don't get is how he never got chucked off here for trolling. I guess it's part of his "special genius" - he knows how to stay impecably on topic while he talks complete rot. I guess you could start a thread here called "I am Jesus Christ, come again", and just keep reating "No, I am Jesus Christ, really, honest", and you're on topic. Have a little literary flight of fancy or whatever like RP does and you'd be trolling.

Oh well. The modding in this place is a mystery to me anyway. I just put some concerns to one of them about that other thread getting moderated indefinitely and some other general suggestions, and got my head bitten off.

Bye Arpie. See you over there, 'cause we're not all here.

[ThinAirDesigns]

Can’t see any purpose to weighing the pressure of the guidance arm at point of contact on the disk or running the cart without a prop.

So, Ynot has now reached the point that he won't just simply do tests folks demand if they don't make sense to him.

Now, I am not critical of that position -- on the contrary, I understand it completely. It should just be noted that this is the *exact* position that when we took it with Ynot he was VERY, VERY critical of.

Ynot ask for many tests that just didn't make sense and when we resisted he wanted to use it against us. He even bragged early in his testing career that "the difference between you and I is I will at least perform the tests others request". LOL -- not anymore I see.

Welcome to the real internet world Ynot, where no effort is enough effort. Now perhaps you understand why we didn't feel the need to perform every silly test you threw our way.

JB

[ynot]

Even though I’ve experienced the evidence firsthand I’ve never quite been able to totally accept that the treadmill and turntable tests accurately represent a cart being powered solely by wind (like many others). So I’ve built a circular wind tunnel to test DDWFTTW in a “real” wind and the cart is only powered by moving air. It’s not high-tech but it works. Things move around quite quickly so you need to use slow motion or frame by frame to see what’s happening.

This video was taken during construction to show and explain the workings . . .

http://www.youtube.com/watch?v=simRdTslucs&feature=channel_page

This video is the wind tunnel and cart in action (the uploaded quality is very poor compared to the original) . . .

http://www.youtube.com/watch?v=oxPegaBWa4o

The cart not only beats the wind it also beats the vanes that create the wind! The series of images below show the flap each time it comes around and you can clearly see that the cart has advanced from vane 4 to vane 1. There is an image missing between the last two because the flap was in the reflection on the plastic and couldn’t be seen. The sequence represents eight revolutions of the cart. It wasn’t taken from the video posted but the same thing can be seen in that video as well.

http://www.accommodationz.co.nz/images/sequence.bmp

The vanes are turned by hand and it’s very easy to keep a constant speed. When the air is up to speed there is very little energy required to retain that speed so the vanes aren’t travelling much faster than the wind. The tunnel is totally enclosed and the air moves essentially as a single mass. The wind created would be at least as constant and stable as an outdoor wind.

[Subduction Zone]

Amazing work ynot. I love your circular wind tunnel. One of the complaints against wind tunnel tests has always been the length of the tunnel. Your version got rid of that objection totally.

[H'ethetheth]

...plus it looks like a hilarious doomsday machine, so double kudos.

[ynot]

Very sorry for the poor video quality. Will try to provide a better quality one as soon as I get time to do so.

[mender]

I'll add my congrats as well, Ynot, good job!

[Michael C]

You've certainly put a lot of work into this. It would be good if you can get hold of a high speed camera in order to view the movement in slow motion.

[ThinAirDesigns]

Ynot = anti-humber. If he doesn't understand something he builds until he does. LOL

Hopefully, since every single test he has done has mirrored the outcome of the simple treadmill test, Ynot can now rest easy that the 4 centuries old principles of Gallilean invariance are still invarient.

Kudos. Very nice work Ynot.

JB

[ThinAirDesigns]

Boingboing #5 comin' up.

JB

[John Freestone]

Kudos, ynot. Very good work. I don't think anyone's ever done that before. Now you need to put a little dog in it and see if it survives. Only joking, pet lovers.

ETA: Maybe Terry should have a ride!

[ThinAirDesigns]

I don't think anyone's ever done that before.

No only that, but his tunnel design I consider to be incredibly creative.

Unfortunately, we are assured to now be bombarded with reasons why his tunnel is flawed and doesn't prove a thing. LOL

JB

[ynot]

Thanks for all the positive feedback.

Haven’t found out how to increase the frame rate on my Sony Handycam yet (if it’s possible) or tracked down a high speed camera that can film in slow motion. In the meantime I thought I would make a close up video that may be a bit easier to view. Not that the overall quality will be any better. I did it in a darkened room to reduce glare on the plastic but unfortunately the internal light is inadequate and things are a bit dark. Thought I would post it anyway as I don’t have time to do it again right now. Have started the video with everything at rest to show the start up. Also removed the top inner cowling so you can see through the tunnel (wasn‘t required anyway). The knocking sound shortly after start up is the tether “tail” hitting the surface it travels over before it settles down. Most of the other noise is the chatter of the gears and wind.

http://www.youtube.com/watch?v=GC-EoGbdyzE (http://www.youtube.com/watch?v=GC-EoGbdyzE)

Yuck! The uploaded video is crap - sorry about that.

[Dan O.]

Thanks for all the positive feedback. Haven’t found out how to increase the frame rate on my Sony Handycam yet (if it’s possible) or tracked down a high speed camera that can film in slow motion.

If you can't get slow motion, you could always try stop motion :)

[CNY_Dave]

Great to see, ynot!


Dave

[ynot]

I’ve been very surprised (almost disappointed) that there hasn’t been any sceptical critsism of the circular wind tunnel. Not that I want to provide a bone to chew on but one of the concerns I had before testing was that the design of the vanes with a circular hole for the cart to pass through might have had some sort of venturi effect that would speed the cart up. The tests disproved this concern but just to confirm I’ve made a video using an impeller instead of the vanes. It’s very hard to get enough overall wind flow using the impeller but you should be able to see that the cart beats the wind even if only by a small amount. The immediate wind coming off the impeller would also be creating a faster wind in the top of the tunnel than the bottom. I may create vanes with just oblong surfaces at the very top and bottom. Would also make the flap and cart easier to see as they travel around.

http://www.youtube.com/watch?v=uTV3DcxKins

Slow motion version of windtunnel3 (thanks to Jeff Reid)

http://www.youtube.com/watch?v=lOINjCtkL0Y

[sol invictus]

I’ve been very surprised (almost disappointed) that there hasn’t been any sceptical critsism of the circular wind tunnel.

The trouble is, the treadmill proves beyond a shadow of a doubt that these carts work (not to mention the trivial physics analysis that shows it's possible). That makes it kind of hard to be skeptical of this.

[ynot]

The trouble is, the treadmill proves beyond a shadow of a doubt that these carts work (not to mention the trivial physics analysis that shows it's possible). That makes it kind of hard to be skeptical of this.
Thing is many people (including myself) were sceptical of the road and treadmill tests. Others were also sceptical of the turntable tests. So far tere hasn't been one person (that I'm aware of) that has been sceptical of the circular wind tunnel tests. Have all the sceptics given up or do they all now accept DDFWTTW is possible? Perhaps they just need time to formulate new arguments against a new test.

[ThinAirDesigns]

Ynot, some will never get it and will just wander off when your experiments work them in the corner. Others will claim "fraud" and just hang around and make fools of themselves -- a couple of those just laughed at your videos when we posted them yesterday. Some folks will not be convinced by anything.

I do have to say the absolute most amusing comment came from the Make magazine forum where a critic says about your video:

Do it in the open air - [no wind tunnel, no treadmill] and you might have something to crow about.
-
ROFLAO! -- it matters not what you do ... someone always wants something different. Do it on the street and they want the tunnel, do it on the treadmill and they want the street. Do it in the tunnel and they want it on the moon.

JB

[sol invictus]

Thing is many people (including myself) were sceptical of the road and treadmill tests.

"Many"? I recall two besides you - humber and Christoff. Not very good company.

But my point was that there is very little room for skepticism here. The treadmill test proves that the cart can go DDWFTTW. You may not believe or understand that, but it is a fact that follows from the most fundamental laws of physics. And it's clear that nothing prevents it from working - there is no law of physics violated by it, one can come very close to it with iceboats tacking into their apparent headwind, one can constuct simple mechanical analogues that work just the same way, etc.

So the only issue initially was whether spork and JB's specific design works - but unless you're a conspiracy theorist unwilling to test anything for himself (which you're obviously not), that would be hard to believe given the evidence.

Others were also sceptical of the turntable tests. So far tere hasn't been one person (that I'm aware of) that has been sceptical of the circular wind tunnel tests. Have all the sceptics given up or do they all now accept DDFWTTW is possible? Perhaps they just need time to formulate new arguments against a new test.

I can essentially guarantee that humber will not accept the results. I very much doubt Christoff will say he does either, if only because if he realizes he was wrong all along he'll simply run away rather than admitting it.

[CNY_Dave]

"Many"? I recall two besides you - humber and Christoff. Not very good company.

But my point was that there is very little room for skepticism here. The treadmill test proves that the cart can go DDWFTTW. You may not believe or understand that, but it is a fact that follows from the most fundamental laws of physics. And it's clear that nothing prevents it from working - there is no law of physics violated by it, one can come very close to it with iceboats tacking into their apparent headwind, one can constuct simple mechanical analogues that work just the same way, etc.

So the only issue initially was whether spork and JB's specific design works - but unless you're a conspiracy theorist unwilling to test anything for himself (which you're obviously not), that would be hard to believe given the evidence.



I can essentially guarantee that humber will not accept the results. I very much doubt Christoff will say he does either, if only because if he realizes he was wrong all along he'll simply run away rather than admitting it.

The scientifically literate part of my brain has no problem with the treadmill, the reptilian part still wants to cry 'foul'. "It's just different", it insists, but I smack it and tell it to go back to snacking on that poor fisherman...

If someone is not able to trust conclusions based on what they've learned vs. what 'seems right' to some dark corner of their brain, they're never going to make any leaps over their innate prejudices.


Dave