Can You Answer This....

[time]

Consider a spiral horizontal coil , center of gravity of which is supported by table at point G. The end of coil E has been brought near point G and a body is hanging right over point G at negligible height but the horizontal coil and body is completely separated by space except at supporting point G. Let mass of spiral coil be m and mass of body be m'. Let length of spiral coil from point G to end E be L. Let speed of compression wave in material of spiral coil be c. The spiral coil, hanging body, table comprises system and intitially the system is in state of static equilibrium. As mass of coil and body is m+m', point G on table is supporting weight (m+m')g.

At t = 0, we begin to release the body and at t = t' the body is completely supported by table at point G and is in state of static equilibrium. That means there is no contact between body and end E of spiral coil. Gravity is acting on this body and weight m'g is acting on point G at t = t'. As the body touches the table, this information will begin to be transmiteed through decompression waves starting from point E to point G and will reach point G after time interval t whete t = L/c. Let total transmission time of compression waves (t) is much much greater than total release time of body(t'). Hence t >> t'. Let blackout time T = t-t'.

During this blackout time T, the point G has absolutely no information about events happening at point E of coil. Hence weight (m+m')g is acting on point G during this black out time T.

So total weight acting on point G during blackout time T is (m+m')g + m'g = (m+2m')g.

Suppose the weight (m+m')g is not enough to break down table at point G. But weight (m+2m')g is enough to break the table.

My question is, will the table break down during blackout time T?

-Abhi.
Email: sciphysics@yahoo.co.in

[davidhorman]

Here's a couple of views of what I imagine you're talking about, is this anything like what you're trying to get across to us?

David

[time]

Originally posted by davidhorman
Here's a couple of views of what I imagine you're talking about, is this anything like what you're trying to get across to us?

David

David, I don't believe it...

I returned to this board and I received first reply from you... Thanks very much.

I know, you have problem understanding the situation, but I really don't know how to draw figure on web page. I will try to learn. Until then, I will prepare doc file which I can send you by email. But I forgot your address...

-Abhi.

[davidhorman]

Abhi, I've PM'd you an email address you can send that document to. I think I'm getting a better idea of what you're trying to describe, but I'll wait until I get your document.

David

[69dodge]

My interpretation: The inner end of the coil is bent down and rests on the table at point G; the rest of the coil doesn't touch the table. The outside end of the coil (E) is bent under the coil so it's near the inner end. The body initially hangs, under the coil and above the table, from E. So the weight of the body is transmitted to the table through the coil. Then the body is released from E and falls to the table near G. Now it is supported directly by the table. But for a short time its weight is still also being transmitted to the table through the coil, until the wave generated by its release reaches the center of the coil from the end. So I think the table will break if it can't support the coil plus twice the body's weight.

[DanishDynamite]

Hmmmm....

For some reason, I'm reminded of a Thin Red Line. (Oldies on the forum will know what I'm refering to :) )

[davidhorman]

For some reason, I'm reminded of a Thin Red Line.

Yup, same guy, no mystery about the name change though. I seem to remember the forum burped and he had to re-register.

Thanks for your interpretation 69dodge - sounds you might have got it. The only simpler (hah) analogy I can come up with might be something like having two fibre optic cables, one a meter long, the other a light-second long, but the longer one is curled up so that the starts and ends of the cables are next to each other.

If you shine a light down the long cable, then move your light over to the short cable in less than a second, for some fraction of a second you will get a combined light output from both cables that is higher than the output of the torch, but only because one signal is delayed.

Dressing it up in this way does make it sound more like a paradox - the object never had enough potential energy to break the table, and yet the table does break. You've delayed the weight of the object by transmitting it through the spiral.

David

[Skeptical Greg]

Originally posted by davidhorman
....
If you shine a light down the long cable, then move your light over to the short cable in less than a second, for some fraction of a second you will get a combined light output from both cables that is higher than the output of the torch, but only because one signal is delayed.....

David

I realize this may not be the point here, but what jumps out at me with this apparent paradox, is that you have to assume zero transmission loss in the fibre optic cables.

If you asume zero loss in any type of system, all kinds of marvelous things will start happening.:)

[davidhorman]

If you asume zero loss in any type of system, all kinds of marvelous things will start happening.

No need to assume zero loss of course - as long as the total loss in both cables is under 0.5, you've still got more light coming out during that length of time t than was ever going in for any other length of time equal to t.

Assumptions can make wonderful things happen, you're right - time was once quite insistant that he'd proved the existence of faster-than-light information transfer, but it all hinged on the pesky false assumption that water is perfectly incompressable.

David

[Skeptical Greg]

Originally posted by davidhorman


No need to assume zero loss of course - as long as the total loss in both cables is under 0.5, you've still got more light coming out during that length of time t than was ever going in for any other length of time equal to t.

Assumptions can make wonderful things happen, you're right - time was once quite insistant that he'd proved the existence of faster-than-light information transfer, but it all hinged on the pesky false assumption that water is perfectly incompressable.

David

I would think the loss in the light second cable would approach 100%..:cool:

If you are aware of a technology that would preclude this, you are more wealthy than you look..:D

[time]

Originally posted by davidhorman
Abhi, I've PM'd you an email address you can send that document to. I think I'm getting a better idea of what you're trying to describe, but I'll wait until I get your document.

David

David, while I am trying to upload doc file to email you, let me post what I have written in it so that others can read it also. But perhaps figure might not look better.
--------------------------
Speed of Propagation of Forces in Newtonian Mechanics

We apply established knowledge of Newtonian mechanics regarding propagation
of forces in bodies. We construct special situation to test whether same
force can act twice at same point during specific time interval due to delay
in propagation of decompression waves carrying information regarding release
of force. If "extra" force of same magnitude is generated due to
propagation delay, then it violates law of conservation of energy. Force is
separated from system, which is in state of static equilibrium, and speed of
compression waves due to mechanical deformation of system is measured from
point of separation of force to supporting point of system. We find that
although decompression waves propagate through system, information regarding
separation of force from system can not propagate through decompression
waves with speed of sound in system.

In Newtonian mechanics, any body, which has mass, can not be perfectly
rigid. Every body has elastic properties to some extent.

(1) Hence in Newtonian mechanics, when we apply force, at one point of body,
it causes deformation of body and this mechanical deformation and
information regarding applied force is communicated to other points of body
through compression waves which propagate with speed equal to speed of sound
in that body.

(2) In Newtonian mechanics, it is also documented that when we release
applied force, again it causes mechanical deformation of body and this
information regarding mechanical deformation i.e. release of force is
communicated to other points of body through decompression waves which
propagate with speed of sound in that body.

We construct special situation to test the validity of second case. We set
out to prove that information regarding separation or release of applied
force to body can not propagate through decompression waves. We do not
attempt to prove existence or non-existence of decompression or compression
waves or it's speed or it's way of propagation.

Description of Special case.

C------------------B-----------------------E-
|S----------------- |-----------------------S |
|S------------------| ----------------------S |
|S------------------|-----------------------S |
|S------------------|control pointA-----S |
|S-------------Hangig Body ------------S |
D-----------------G--------------------------F
-------------------||-------------------------
==Table====M========================
=====================================
[hope that above figure will look better to you]

As shown in above figure, square shaped system of lines DCBEFG is placed on
table in such a way that it is supported by small plate GM at mid-point M of
table. Vertical line AB is attached to point B of system. At point A, a
body is attached by very small string and control mechanism at point A can
lift or release the body. The body attached to point A is just hanging right
over point G at negligible height from point G. No part of system is
touching the table except at point G, which is supported by plate GM.

Lines AB, BC, CD, DG, GF, FE, BE, plate GM, body, table etc can be made of
any material, any shape which is convenient for understanding.

The whole system is in state of static equilibrium. Let mass of system,
excluding body, be m and mass of body be m'. Let length of lines ABCDG and
ABEFG be L each. Let speed of compression wave in material of system be c.
As mass of system and body is m+m', point M on table is supporting weight
(m+m')g.

At t = 0, we begin to release the body very slowly using control mechanism
at point A and at t = t' the body is completely supported by plate GM on
table at point M and is in state of static equilibrium. That means there is
no contact between body and control mechanism at point A whatsoever. We call
this time interval t' as release time. As the body is still under
gravitational field, gravity is acting on this body and hence weight m'g is
acting on point G and through plate GM, at point M of table at t = t'. As
the body touches point G and hence will be supported by table through plate
GM.

This will cause release in strain at point A and this information will begin
to be transmitted through decompression waves starting from point A, to B,
C, D and to point G on left side of system. On right side of system,
decompression will propagate from point A to B, E, F and to point G. As
length of segment ABCDG is L and length of segment ABEFG is also L,
decompression waves will reach point G after time interval t where t = L/c.
Length L of each segment is such that total transmission time of
decompression waves t is far greater than total release time of body t'.
Hence t >> t'. Let difference between total transmission time and release
time be T = t-t'. We call this difference T as time delay.

During this time delay T, the point G and M has absolutely no information
about events happening at point A of system. Even though the weight m'g of
body is acting on point M during delay time T, point M has absolutely no way
to "know" that the body was earlier hanging at point A of system. This point
M will only come to know about it after decompression waves reaches point M
after time interval t. Until that moment this body will be treated as second
body which is brought from outside the system. So we find that during this
time delay T, weight = (m+m')g + m'g = (m+2m')g is acting on point M of
table even though mass of system and body is just (m+m').

Suppose the weight (m+m')g is not enough to break down table at point M. But
weight (m+2m')g is enough to break the table. Hence the table will break
down during time delay T. This is in sharp contrast to law of conservation
of energy because we find that extra force m'g is generated due to
propagation delay of compression waves. In this way, as we use this extra
force to break the table, we can use it to do any "extra" work we want.

Example:

Suppose, instead of body, it is you hanging at point A of system. Let your
mass be 100 Kg and that of system be 100 Kg. You are hanging right over
point G in such a way that distance between your feet and point G is just
fraction of millimeter. So weight acting on point M of table is (100 +100)g
N.

(1) Now at t = 0, you leave point A and jump outside table on ground. As
your mass is 100 Kg, force equal to 100g N is separated from system. This
will cause release of strain and mechanical deformation at point A. of
system. In Newtonian mechanics, this information will propagate across
transmission lines of system. Let it take 10 seconds to reach these waves to
point M of table. So during these 10 seconds, gravitational force (100+100)g
N is still acting and point M of table is still exerting upward force of
same magnitude because point M has no information regarding separation of
your mass and gravitational force.

(2) But you change your intentions and at t = 0, instead of jumping outside
table, you jump on point G of system, which is just fraction of millimeter
from your feet. Even if you release point A of system and standing on point
G, gravity is still acting on you. As your mass is 100 Kg, gravitational
force equal to 100g N is acting on point G and hence point M. But the moment
you leave point A of system, information regarding separation of your force
begin to propagate on its long journey of 10 seconds.

Central idea is, how the point M of table will know during these 10 seconds
that your body was previously hanging at point A and it should not
experience your weight twice because it is already experiencing it?

The only way to know it in Newtonian mechanics is decompression waves. These
waves are taking long path to propagate and reach to point M. Before these
waves reach point M, information regarding weight of your body is taking
very short path through your feet directly to point M of table.

So during these 10 seconds, weight 200g N is acting on point M of table just
like it was acting at t = 0. But during these 10 seconds, your weight 100g N
is also acting on point M of table. So during these 10 seconds, total weight
acting on point M of table is 200g + 100g = 300g N. Suppose table can break
down only after applying weight of 300g N at point M. Then we see no reason
why the table will not break down during these 10 seconds. In this way we
can break any body which is supposed break at 300g N force by using just 200
Kg mass. This is in sharp contrast of law of conservation of energy.

Conclusion:

We conclude that information regarding separation or release of applied
force, be it gravitational force or mechanical force, does not propagate
through decompression waves with speed of sound in system. Hence we prove
that second case of Newtonian mechanics, as stated out in introduction part
above, does not hold true.

-Abhi.

[time]

Originally posted by 69dodge
My interpretation: The inner end of the coil is bent down and rests on the table at point G; the rest of the coil doesn't touch the table. The outside end of the coil (E) is bent under the coil so it's near the inner end. The body initially hangs, under the coil and above the table, from E. So the weight of the body is transmitted to the table through the coil. Then the body is released from E and falls to the table near G. Now it is supported directly by the table. But for a short time its weight is still also being transmitted to the table through the coil, until the wave generated by its release reaches the center of the coil from the end. So I think the table will break if it can't support the coil plus twice the body's weight.

You undrstood the problem..

So you think that extra force = m'g will be generated due to propagation delay. Let us see what others say..

-Abhi.

[davidhorman]

I've attached the diagram from Abhi's document which should make things clearer.

But there's no mystery here. Look at my laser example - I don't think anyone would deny that what I've described is what would happen (except Diogenes ;) ) but it certainly seems paradoxical. Beyond that I'm not going to devote any more brain power to this right now, so if anyone else would like to have a bash at explaining this to Abhi, go ahead.

David

[time]

Originally posted by DanishDynamite
Hmmmm....

For some reason, I'm reminded of a Thin Red Line. (Oldies on the forum will know what I'm refering to :) )

Yes, I am the same "Thin Red Line". Perhaps you remember, in old days user ID and name displayed on forum were different. Then one day administrator changed everything and user ID was being displayed on forum.

This created some problems at that time to some people, I remember. Time is my old User ID. I havn't registered freshly.

-Abhi.

[time]

Originally posted by davidhorman
I've attached the diagram from Abhi's document which should make things clearer.

David

You have surprised me few times before. I am really surprised once again how fast you did it..

-Abhi.

[davidhorman]

I am really surprised once again how fast you did it..

Girls are always saying that to me :confused:

If this makes any sense, the total force supported by the table during the time of the experiment is equal to the total force exerted by the mass. All you've done is shift some of it in time by delaying it in the structure of the support frame. This is balanced out because when you first attach the weight to the frame, the table doesn't start supporting it until the "signal" has been transmitted through the frame.

Yes, in theory you could use this method to do "extra work" at a particular time, but you'd find you'd be able to do less work later (or is that earlier?), so everything checks out, everything balances, and you haven't proved anything ground-breaking.

Anyone else want to have a go? I never feel like I do a good job of explaining things.

David

[69dodge]

Originally posted by time
In this way we can break any body which is supposed break at 300g N force by using just 200 Kg mass. This is in sharp contrast of law of conservation of energy.The law of conservation of energy is about energy, not force. They're not the same. There's no law of conservation of force.

I weigh less than 150 pounds. My car weighs more than 3000 pounds. I can lift my car, with the help of a bumper jack.

[time]

Originally posted by davidhorman
If this makes any sense, the total force supported by the table during the time of the experiment is equal to the total force exerted by the mass. All you've done is shift some of it in time by delaying it in the structure of the support frame. This is balanced out because when you first attach the weight to the frame, the table doesn't start supporting it until the "signal" has been transmitted through the frame.
First Case:

Suppose initially, the point M is supporting only weight of system mg. It is correct that when you first attach the body, the signal will take time to reach to point M of table. So during this propagation delay, the point M is balancing only weight mg and not (m+m')g N. I agree.

But in such situation, even if you use that weight m'g which is propagating across system and weight mg at point m of table, it does not violate law of conservation in any way. There is no extra weight or force generated in this first case.

Second Case:

In situation I have described, we get extra force generated due to propgation delay. And we get time to use it. Point M has no way to know that extra force is generated and it should not break.

So first case does not violate law of conservation of energy, but second case does violate law of conservation of energy.

I can give you following anology:

Suppose you have just one billion dollar in your bank a/c and other one billion dollar deposited by you in bank is in transit and not credited to your a/c by bank. If you spend that other one billion dollars while it is in transit and even if bank has not given credit to you, it is not "free" dollars. It is hard earned by you.

But if you have already two billion dollars in your a/c and you transfer one billion dollar from a/c A to a/c B. Now bank give credit of one billion dollar to a/c B first and debit one billion dollar to a/c A much later due to propagation delay of processing. So you have two billion dollar in a/c A and one billion in a/c B. So you got three billion dollars. Now you can withdraw three billion dollars and spend that "extra free" one billion dollar.

Even if bank realise this mistake later, the damage is already done. You got it....

-Abhi.

[DrMatt]

It's long been known that forces can be momentarily concentrated due to the timing and phasing of waves. Much of acoustics deals with this.

But the total energy output never exceeds the input.

[davidhorman]

Even if bank realise this mistake later, the damage is already done. You got it....

Unforunately there is no law of conservation of cash. Money was invented by man and isn't subject to the laws of physics (any Arthur Andersen accountant can tell you that). My economics teacher once explained to me how money is created - something you can't do with energy.

69dodge has made a great point - there is no law of conservation of force, only a law of conservation of energy.

Look at my optical cable example again. Suppose you had a detector which would open a door when you shine, I don't know, 2000 photons on it over a period of 1 second. Your torch only emits 1500 photons per second, for ten seconds. Well, you just use your really long optical cable and delay some of your photons.

Your torch will emit a total of 15000 photons. All 15000 will reach the detector. If you redirect a second's worth of those photons (1500) through that light-second long cable, you can delay them by a second and combine them with another 1500 photons that have taken the direct route. Voila, 3000 photons and the door opens.

The door opens. The table breaks. For a moment your peak output has exceeded your peak input, but energy is conserved.

What's the problem?

David

[Lesault]

Originally posted by davidhorman


The only simpler (hah) analogy I can come up with might be something like having two fibre optic cables, one a meter long, the other a light-second long, but the longer one is curled up so that the starts and ends of the cables are next to each other.

If you shine a light down the long cable, then move your light over to the short cable in less than a second, for some fraction of a second you will get a combined light output from both cables that is higher than the output of the torch, but only because one signal is delayed.

Dressing it up in this way does make it sound more like a paradox - the object never had enough potential energy to break the table, and yet the table does break. You've delayed the weight of the object by transmitting it through the spiral.

David

You would get more light than the output of the torch, but for less time...
Suppose you shine (all) the light from the torch into the long fibre for 1 second until it starts coming out the other end, you then immediately move the torch over to the short fibre. You will get twice the amount of light* coming out of the combined fibres for 1 second until all the light in the long fibre is 'used up' then the light drops to whatever is coming out of the short fibre.
You have, then, had 1 second of the double-intensity light, but the torch has been shining for 2 seconds in total. During the first second no light is coming out of the fibres. No paradox.

*assumes no loss in the fibres.

Lesault

[time]

Originally posted by davidhorman

69dodge has made a great point - there is no law of conservation of force, only a law of conservation of energy.
David

David, I have devised following experiment to test what I am saying. Is there any flaw?
--------------------
This experiment is initially intended to prove that information regarding separation or release of applied force to body can not propagate through decompression waves with speed of sound.

We use very long transmission line made of any material in which information regarding release of applied force is supposed to travel in accordance with established knowledge of physics. The force is applied to starting point A of transmission line and "end point B of transmission line is exactly at same level of starting point A" (where force is applied) of transmission line. We apply established knowledge of physics to calculate propagation delay time taken for information regarding release of applied force to travel from starting point A to end point B of transmission line.

If during this propagation delay time, end point B of transmission line does not move in space, then established knowledge of physics is correct. But if end point B of transmission line moves in space during this propagation delay time, then we show that information regarding separation or release of applied force to body does not propagate in accordance with established knowledge of physics.

We use high-speed video camera focused on starting point A and end point B of transmission line and electronic clock in the background. We check every frame of video film in slow motion to see whether end point B of transmission line is displaced in space during propagation delay time or not.

If end point B of transmission line moves in space during this propagation delay time, then we go on proving validity of following principle.

"When the system is in state of static equilibrium and if we release applied force (Gravitational force, mechanical force, magnetic force etc.) to a body, this information regarding release of applied force is transmitted to every point of body instantaneously".

----------------

-Abhi.

[davidhorman]

Your experiment sounds fine to me. But...

The speed of sound in a material is essentially defined as the speed a force is transmitted through it. What is sound, after all? It's a longitudinal wave. How do you set a sound in motion through an object? You apply a force to it. For a human to make a noise it's the combination of lungs and vocal chords that apply this force to the air. The signal then travels through the air at 330m/s, or thereabouts.

Also, consider this: in crash tests, the target car crumples when subjected to the force of impact. Why? Because the "signal" that the front end of the car has been hit can't be instantly trasmitted through to the back end, because the material the car is made of has a finite Young modulus and non-zero mass/inertia.

By all means, try your experiment. All you'd be measuring is the speed of sound by another name, and that's rather well known for most materials already.

David

[rwguinn]

Originally posted by davidhorman
Your experiment sounds fine to me. But...

The speed of sound in a material is essentially defined as the speed a force is transmitted through it. What is sound, after all? It's a longitudinal wave. How do you set a sound in motion through an object? You apply a force to it. For a human to make a noise it's the combination of lungs and vocal chords that apply this force to the air. The signal then travels through the air at 330m/s, or thereabouts.

Also, consider this: in crash tests, the target car crumples when subjected to the force of impact. Why? Because the "signal" that the front end of the car has been hit can't be instantly trasmitted through to the back end, because the material the car is made of has a finite Young modulus and non-zero mass/inertia.

By all means, try your experiment. All you'd be measuring is the speed of sound by another name, and that's rather well known for most materials already.

David
The speed of force propigation through a spring is 1/fn seconds, where fn is the natural frequency of the system. There is a phase shift (delay), but if you measure reaction force, it will track right along with the oscillation of the system- just out of phase.
When part of the mass is removed, the frequency goes up. So, at the time of release, the frequency of the system increases dramatically (f=1/(2*pi)*(k/m)^.5), but the time delay is there due to the phase shift- the table breaks (assuming the length of time for m' to reach the table is less than the new value of fn).
That is one reason why we add a "dynamic ringing factor" to static loading when necessary.
The car crumples because the inertia loading by the part still moving, applied to the zero-velocity chunk, exceeds the yield strength of that chunk-again, phase shift. A simple experiment - place an empty beer/soda can upright on the ground. set a concrete block on the can. It will support it, no problem. Now, drop the block from a height of 6 inches or more. oops!
RW

[davidhorman]

rwguinn, you can take over :) You obviously know a lot more about this than me!

David

[rwguinn]

Originally posted by davidhorman
rwguinn, you can take over :) You obviously know a lot more about this than me!

David
I ain't takin over NOTHIN!
20 years of rocket science and 6 analyzing busses gives you just enough knowlege to be dangerous....:D

RW