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View Full Version : Physics assistence por favor

30th August 2006, 12:07 PM
From a CTist
A car weighing 18,000 Newtons going 40 Km/h hits a stopped car weighing 14,000 Newtons. The two cars travel off together. In the absence of friction how fast would they move off?

who knows physics?? More specifically who knows conservation of momentum??

Prove it by answering the above question. After that I will get the exact numbers I need and will prove that 9/11 had to involve an alternate energy source/no pancake theory. If someone else can get me exact numbers like weight of building and distribution of weight. number of floors the plane crashed through. height of building and height of each floor including the ceilings. Things like that and the exact time it took the building to fall. I have done this loosely before with semi real numbers and the buildings should have fallen about 10 seconds longer based off theose estimates.

The physics that took place on 9/11 make no sence. Unless the floors below the crash offered about 0 resistence.

conservation of momentum was violated on 9/11 based off physics and the official report.
One conclusion can come out of that, and it is not that physics all the sudden changed. It is that the official story is a fairytale.

I will post the answer below.

Hazzard failed
DEBUNKER failed

Yet they Knew I was not right about my physics. KNEW.

************************************************** **************

initial mass = 18,000/9.81 (F=ma) = 1835 Kg
initial velocity = 40/3600 X 1000 (1000m/km and 3600s/h) = 11m/s
11 X 1835 = 20185 Kgm/s
mass2 = (14,000 + 18,000)/9.81 (F=ma) = 3262 Kg

so using conservation of momentum: m1 X v1 = m2 x v2
you would see that since there was more mass after the crash the speed would be less.

3262 X v2 = 20185

OR

v2 = 20185/3262

so resulting velocity of the two cars traveling off together would be around 6.2 m/s or 22.32 Km/h in the direction the first car was moving.

Want to try again hazzard?
I can add friction of the road to the tires and they could crash on an incline. I could say the cars were in contact for a certain amount of time and how would that matter?

This post has been edited by muddyfrog: Today, 02:00 PM

The thing that jumps out at me is the first sentence; Newtons are a measurement of force, not weight, correct?

Hellbound
30th August 2006, 12:20 PM
Arkan:

Weight is a measure of force, specifically a measure of the force with which gravity is pulling you.

THe math looks right, actually.

However, what he leaves out is that the material falling from WTC was NOT moving at a constant velocity, it was being CONSTANTLY accelerated. And with each floor hit, it became more massive, meaning the next floor's resistence would slow it down less (using those same momentum laws, as the amount of mass at rest decreases compared to the amoutn of mass in motion, it has less effect on the final velocity).

30th August 2006, 12:24 PM
Arkan:

Weight is a measure of force, specifically a measure of the force with which gravity is pulling you.

THe math looks right, actually.

However, what he leaves out is that the material falling from WTC was NOT moving at a constant velocity, it was being CONSTANTLY accelerated. And with each floor hit, it became more massive, meaning the next floor's resistence would slow it down less (using those same momentum laws, as the amount of mass at rest decreases compared to the amoutn of mass in motion, it has less effect on the final velocity).

So, he was using Newtons just to be a smart@\$\$? For clarification, below the ****** was Hazzard's post, which muddytoad claims is wrong.

Hellbound
30th August 2006, 12:29 PM
YEah, he used Newtons to be a smart@\$\$, or (more likely, since he called the math up there wrong) he doesn't understand the difference between weight and mass.

The math up there looks right, though. IF that's HAzzard's, he knows what he's saying.

30th August 2006, 12:35 PM
Thanks much! :D

TK0001
30th August 2006, 12:37 PM
Thanks much! :D

I had a feeling you'd pick that one up. ;)

Hellbound
30th August 2006, 12:37 PM

Se this high school physics site (http://www.glenbrook.k12.il.us/GBSSCI/PHYS/Class/momentum/u4l1a.html).

Momentum = mass * velocity. Fairly simple.

What Hazzard did was take the weight in Newtons (which is a force) and apply Newton's llaws to it: Force = mass * acceleration. Since, in a weight, the acceleration is gravity, this means the weight in Newtons divided by 9.81 gives the mass in kilograms.

Now, momentum pre-crash should equal momentum post-crash, so mass * velocity of the single car travelling shoudl equal the mass * velocity of both travelling, which is what Hazzard proceeeded to do.

Muddytoad doesn't know his physics from his anus (which seems to be where he gets his physics from).

RenaissanceBiker
30th August 2006, 12:38 PM
Well, all those constants like g and the velocity conversions cancel out. You could just say:

V = 18 kN * 40 km/h / (18 kN +14 kN) = 22.5 km/h

/professional engineer

Hellbound
30th August 2006, 12:38 PM
Well, all those constants like g and the velocity conversions cancel out. You could just say:

V = 18 kN * 40 km/h / (18 kN +14 kN) = 22.5 km/h

/professional engineer

Yeah, if you wanna do it the EASY way!

:D

30th August 2006, 12:40 PM
Well, all those constants like g and the velocity conversions cancel out. You could just say:

V = 18 kN * 40 km/h / (18 kN +14 kN) = 22.5 km/h

/professional engineer

Seeing as how I haven't done physics in 15+ yrs, mind if I snag that verbatim? (I have asked muddytoad for clarification on whose text is below the asterisks)

RenaissanceBiker
30th August 2006, 12:58 PM
Seeing as how I haven't done physics in 15+ yrs, mind if I snag that verbatim? (I have asked muddytoad for clarification on whose text is below the asterisks)

Just give me credit and buy me a beer if you ever get a chance.

Darth Rotor
30th August 2006, 01:15 PM
Just give me credit and buy me a beer if you ever get a chance.

Isn't conservation of momentum less than 100% efficient for non-rigid bodies, making
M(2)V(2) < M(1)V(1)
for most collisions?

For example, cars' bodies absord "x" amount of energy into their frame, deforming the metal, so that energy used for deformation is not transfered into momentum a la M*V.

Right?

See also golf balls and wooden, forged, or cast clubs, versus the harder (titanium) club faces of the current driver genre.

Entropy can wait for another time.

DR

defaultdotxbe
30th August 2006, 01:19 PM
Isn't conservation of momentum less than 100% efficient for non-rigid bodies, making
M(2)V(2) < M(1)V(1)
for most collisions?

For example, cars' bodies absord "x" amount of energy into their frame, deforming the metal, so that energy used for deformation is not transfered into momentum a la M*V.

Right?

See also golf balls and wooden, forged, or cast clubs, versus the harder (titanium) club faces of the current driver genre.

Entropy can wait for another time.

DR

yes, the real world is indeed much more complex than HS physics :)

30th August 2006, 01:20 PM
Isn't conservation of momentum less than 100% efficient for non-rigid bodies, making
M(2)V(2) < M(1)V(1)
for most collisions?

For example, cars' bodies absord "x" amount of energy into their frame, deforming the metal, so that energy used for deformation is not transfered into momentum a la M*V.

Right?

See also golf balls and wooden, forged, or cast clubs, versus the harder (titanium) club faces of the current driver genre.

Entropy can wait for another time.

DR

Considering muddytoad has already come up with the gem of "I have done this loosely before with semi real numbers and the buildings should have fallen about 10 seconds longer based off theose estimates.

The physics that took place on 9/11 make no sence. Unless the floors below the crash offered about 0 resistence." I don't know that we need too much detail.

deja vu by the way

RenaissanceBiker
30th August 2006, 01:26 PM
Yes, Darth Rotor, but the problem was stated in the simplest terms. If you are going to ignore friction you are probably ignoring those other pesky little details as well. This is the high school physics solution, not the PE exam solution. That one would require more information.

I'm not sure how muddytoad plans to apply this to his CT of the WTC collapse. I'm almost positive it will be incorrect.

rwguinn
30th August 2006, 02:20 PM
Arkan:

Weight is a measure of force, specifically a measure of the force with which gravity is pulling you.

THe math looks right, actually.

However, what he leaves out is that the material falling from WTC was NOT moving at a constant velocity, it was being CONSTANTLY accelerated. And with each floor hit, it became more massive, meaning the next floor's resistence would slow it down less (using those same momentum laws, as the amount of mass at rest decreases compared to the amoutn of mass in motion, it has less effect on the final velocity).

er--nevermind.. I just saw the "compared to the amoutn of mass in motion" part.
you are correct--you only have to deal with the mass of one floor at a time doing the resisting, while the to-be-resisted grows with the addition of each floor...

boooeee
30th August 2006, 02:41 PM
Isn't conservation of momentum less than 100% efficient for non-rigid bodies, making
M(2)V(2) < M(1)V(1)
for most collisions?

For example, cars' bodies absord "x" amount of energy into their frame, deforming the metal, so that energy used for deformation is not transfered into momentum a la M*V.

Right?

See also golf balls and wooden, forged, or cast clubs, versus the harder (titanium) club faces of the current driver genre.

Entropy can wait for another time.

DRNot exactly. Conservation of kinetic energy is not 100% effecient for non-rigid bodies. When two non-rigid bodies collide, some of their energy is dissipated through heat. However, the total momentum is 100% conserved, assuming they're on a frictionless surface.

I'm being nitpicky, but your post above seemed to indicate that momentum could be lost due to the two cars interaction with eachother. Momentum is only lost if the two cars interact with an outside body (e.g. the ground).

CurtC
30th August 2006, 03:26 PM
Not exactly. Conservation of kinetic energy is not 100% effecient for non-rigid bodies. When two non-rigid bodies collide, some of their energy is dissipated through heat. However, the total momentum is 100% conserved, assuming they're on a frictionless surface.
And those of us who are really picky point out that momentum is 100% conserved, even counting friction; you just have to include the Earth in the calculations.

boooeee
30th August 2006, 03:36 PM
And those of us who are really picky point out that momentum is 100% conserved, even counting friction; you just have to include the Earth in the calculations.True, true. I meant the momentum of the two bodies only. But I can hardly complain about nitpicks at this point.

Reminds me of one of my favorite physics brain teasers: If England changed it's driving laws such that everybody had to drive on the right side of the road, would the day get shorter, longer, or stay the same?

tracer
30th August 2006, 03:58 PM
Reminds me of one of my favorite physics brain teasers: If England changed it's driving laws such that everybody had to drive on the right side of the road, would the day get shorter, longer, or stay the same?
The day would get longer, for a while, because all the road workers would have to put in a huge amount of Overtime changing the signs around.

R.Mackey
30th August 2006, 04:43 PM
So, he was using Newtons just to be a smart@\$\$? For clarification, below the ****** was Hazzard's post, which muddytoad claims is wrong.
Looks like you've already got your answer. Conservation of Momentum is correct, mboth vboth = m1v1 + m2v2, the rest of the kinetic energy is dissipated by smashing up the cars.

Newtons is correct. In metric, you measure weight in Newtons. However, what you really want in the Conservation of Momentum equation is mass, so you need to divide by 10 kg / N -- Ok, it's 9.8 m/s2, but 10 is close enough -- to get the mass. His answer wasn't a smartazz answer, just not elegant.

The whole "Conservation of Momentum" argument denying the pancake theory is precisely the drivel that Gordon Ross has put forth, as seen in the June issue of the "Journal for 9/11 Studies" linked through "Scholars for 9/11 Truth." (http://www.st911.org/) I note some blatant hypocrisy in that the "Journal" is not peer-reviewed, contrary to the claim in their portal... truth indeed... Anyway, Dr. Greening does a good job taking Ross to task, and Ross is still trying to get the last word.

I've critiqued Ross's paper myself, first in this post (http://forums.randi.org/showthread.php?postid=1822297#post1822297) and then addressing the follow-ups, as Greening rebuts and Ross still gets it wrong, here (http://forums.randi.org/showthread.php?p=1829989#post1829989). The problem with arguing against pancake collapse via a momentum and energy conservation argument is that the problem is difficult to set up completely -- this is Gordon Ross's mistake. His argument is that the lower part of the WTC tower would rebound elastically when hit to match the speed dictated by conservation of momentum, this rebound sinks a good chunk of the kinetic energy, and the net result is just barely under the failure energy required to destroy another floor. What he leaves out is that the new kinetic energy must then be dissipated as well -- he stops the calculation with several floors still moving downward, no lie -- and that transmitting energy to make floors below the contact floor also rebound induces further strain on the support columns, due to the floors' inertia, that he doesn't account for.

Ross also makes some bad assumptions about how much of the structure will sense the collision and rebound before the top starts to crumble. He further insists on other events that must take place before failure must progress (like crushing both contact floors completely to powder) that are clearly not required. In his zeal to add detail to the situation, he leaves out several important components of the true energy balance. I'll give him the benefit of the doubt and say that it was a series of honest mistakes, the kind that would have been caught were this a true peer-reviewed journal. Or if they sought any criticism at all.

To relate this to your crashing cars example, crashing the two cars on a frictionless surface makes the calculation easy, but it isn't a good model for our system. ("Easy, but wrong.") The WTC towers were fixed on the ground. The various floors are coupled with elastic (and then plastic, after being driven beyond their elastic limits) columns. Think of it instead as crashing one car into another that's held fixed by a stiff spring, a spring that breaks once either its stress or its strain exceeds a certain value.

I don't have much confidence the CTer in question will be able to set this problem up correctly given what you've shown me so far. Big surprise, I know.

fuelair
30th August 2006, 05:09 PM
Yes, Darth Rotor, but the problem was stated in the simplest terms. If you are going to ignore friction you are probably ignoring those other pesky little details as well. This is the high school physics solution, not the PE exam solution. That one would require more information.

I'm not sure how muddytoad plans to apply this to his CT of the WTC collapse. I'm almost positive it will be incorrect.

And without friction or gravity (towers, not cars) how is this related??

gumboot
30th August 2006, 11:25 PM
The day would get longer, for a while, because all the road workers would have to put in a huge amount of Overtime changing the signs around.

Actually one of the Scandanavian countries did it overnight... (was it Sweden???).

-Andrew

RenaissanceBiker
31st August 2006, 04:50 AM
Look at it this way, if we only look at conservation of momentum and ignore conservation of energy, nothing would ever fall. The upper floors of the WTC had a downard velocity of zero before the supports were taken out. Once the thermite charges built into the structure detonated, the downward momentum would remain zero.

The apple in Newton's tree had an initial downward momentum of zero. There's no way it could have fallen by itself. It had to have been pushed! Now we know the conspiracy goes back over 200 years!

gumboot
31st August 2006, 05:03 AM
The apple in Newton's tree had an initial downward momentum of zero. There's no way it could have fallen by itself. It had to have been pushed! Now we know the conspiracy goes back over 200 years!

The apple fell because the thermite larvae inside it ate its core...

-Andrew

NobbyNobbs
31st August 2006, 05:12 AM
The fact that he used weight instead of mass doesn't bother me, because *everybody* mixes those two up. In fact, I was surprised he got the units for weight right. Then I got to thinking: why did he use Newtons? Not very many people (in the U.S., at least) have a good idea how much a Newton is. So I did some conversions...

18,000 Newtons=39,600 pounds, or a little under 20 tons.
14,000 Newtons=30,800 pounds, or almost 15.5 tons.

What kind of car is this guy driving???

RenaissanceBiker
31st August 2006, 05:39 AM
The apple fell because the thermite larvae inside it ate its core...

-Andrew

The larvae was intentionally placed in the apple core as it grew. That's why there was no evidence of a larvae insertion point.

It's true.

jhunter1163
31st August 2006, 05:50 AM
A car weighing 18,000 Newtons going 40 Km/h hits a stopped car weighing 14,000 Newtons. The two cars travel off together. In the absence of friction how fast would they move off?

I don't think cars made of Newtons would be very rigid. They would have very large crumple zones too. On the other hand, cleanup after accidents could be accomplished by an elementary school class with a few gallons of milk.

gruk
31st August 2006, 05:52 AM
Actually one of the Scandanavian countries did it overnight... (was it Sweden???).

-Andrew

Yep, September 1967.

Wikipedia article (http://en.wikipedia.org/wiki/Dagen_H)

NobbyNobbs
31st August 2006, 07:06 AM
The fact that he used weight instead of mass doesn't bother me, because *everybody* mixes those two up. In fact, I was surprised he got the units for weight right. Then I got to thinking: why did he use Newtons? Not very many people (in the U.S., at least) have a good idea how much a Newton is. So I did some conversions...

18,000 Newtons=39,600 pounds, or a little under 20 tons.
14,000 Newtons=30,800 pounds, or almost 15.5 tons.

What kind of car is this guy driving???

Oops. I was using the wrong conversion factor. Please ignore the above.

18,000 Newtons is 2 tons. 14,000 Newtons is 1.5 tons. Much more reasonable.

RenaissanceBiker
31st August 2006, 07:20 AM
Ah, yes. You were using Figanewtons.

Darth Rotor
31st August 2006, 07:24 AM
:D A car weighing 18,000 Newtons going 40 Km/h hits a stopped car weighing 14,000 Newtons. The two cars travel off together. In the absence of friction how fast would they move off?

I don't think cars made of Newtons would be very rigid. They would have very large crumple zones too. On the other hand, cleanup after accidents could be accomplished by an elementary school class with a few gallons of milk.
That would be "crumble zones" but otherwise I completely concur with your analysis.

Disclaimer from Nabisco: These analyses were performed by professional skeptics. Don't try this in your own home. No Fig Newtons were actually harmed during these analyses, although a few brain cells were killed by colleral beer damage.

DR

31st August 2006, 11:21 AM
fwiw, from a good friend of mine who is an ME at Bridgestone/Firestone

Okay, I think I remember this.

Mo*v = Mo*v
Mo of moving car: 18000 * 40 = 720000
(18000+14000)*v = 720000
V=22.5 kph

So assuming no energy is lost and the all mass is conserved in the
system (i.e. drivers are not ejected from car, etc), the jumbled mess
will move off at a stately 22.5 kph (14mph) across your hypothetical
frictionless surface.

This, of course, makes me curious as to the question of "Exactly how
good are the energy absorbing 'crumple zones' in soaking up the Mo?"
Let alone the energy lost in vehicle/ground friction and whatnot.

31st August 2006, 11:38 AM
Oh, and muddytoad clarified, the numbers in the bottom of his/her post are his/her calc's, not that of Hazzard.

jskowron
31st August 2006, 12:04 PM
Even assuming the physics/math were correct, the CT logic would still be along the lines of

"since two outrageously huge automobiles crashing into each other would have this velocity......the government must have blown up the WTC buildings"

They resort to physics/math to appear to be more of an authority than they are, and to introduce a strawman (e.g. "your book physics can't perfectly explain the ultra-complex, real world, probably never before thought of collapse of giant skyscrapers that have been hit by jets, and since it is unlikely that "physics" is wrong, the official explanation of what happened must be.")

31st August 2006, 02:24 PM
fwiw, from a good friend of mine who is an ME at Bridgestone/Firestone

Minor correction has been passed along to me:

Well, if you use this in a post, I made a typo. Momentum = Mass *
Velocity. So its M*V = M*V, not Mo*V = M0*V. I was overzealous typing
out my Mo's.

As always, transparency is the best policy.

Verde
31st August 2006, 03:14 PM
If England changed it's driving laws such that everybody had to drive on the right side of the road, would the day get shorter, longer, or stay the same?

As I recall, the actual discussion about this had the buses and lorries moving over first as a test period, and if successful the cars would change over the following month.