If C is the Speed Limit, Does That Prove Universal Elasticity?

[Prometheus]

Wierd question. I was thinking about it today at work while feeling vibrations from over a mile away on an oil pipeline I was building.

Any physicist will tell you that no object or influance can travel faster then the speed of light.

If you take a rubber rod set on a table, and hit the end with a hammer, the end that is struck will move forward, and when the compression wave reaches the other end it will move as well. If you hit a rod of wood (less elastic) the compression wave moves faster, and a steel rod is even faster. All of these materials have enough elasticity, that is you move one end, the other end moves a fraction of a second later, because the compression wave must move through the material.

Now imagine a rod of a material that is totally inelastic. The influence on one end would move to the other end immediately, and would break the speed of light rule.

So according to this, there is no perfectly innelastic substance, right?

Any thoughts?

[Jack]

there is no perfectly innelastic substance, right?

You obviously have never viewed my monthly household budget.

From a discussion of rebounding between two perfectly inelastic substances:

you have also, in a way, asked about the behavior of perfectly rigid objects. Even though there is no such thing, we can still arrive at an Answer for that, too. Consider that when any object experiences an impact, there is some magnitude of Force involved in that event. Well, Force equals Mass times Acceleration, or (F)=(m)(a), and so that Force of impact can be expected to lead to some Acceleration and motion of the Mass-possessing object. This Law of Physics does not change if the object happens to be infinitely rigid! Let us return to an ordinary elastic object for a moment. As a Force of impact occurs, the portion of the object where the impact happened will experience some compression, as you know. But there is more! That "essence of compressed material" is not a stationary thing! The Force of impact actually causes a WAVE of compression to begin moving through the body of the object. This wave can be thought of as the mechanism by which the Force is "felt" by every portion of the object. The speed of this wave will equal the speed of sound in the substance of the object, and for most solid objects, this is easily more than a couple of kilometers per second. After less than a thousandth of a second, for most ordinary objects, the entire object begins moving as a whole thing, rebounding from the Force of impact. Finally, regarding the hypothetical infinitely rigid object, a logical consequence is that the speed of sound in the object will be equal to infinity. There will be no compression wave, but the whole object will be instantly affected by the applied Force! It will rebound in accordance with (F)=(m)(a) WITHOUT storing any energy!

Source

[SoccerfreakAB2]

Nice question prometheus, although unfortunately I can't think of anything that would fit total elasticity.

[Prometheus]

So it's already assumed to be imposible by physicists? How do they prove it (i'm assuming they have a better proof then mine)? Is it because of the nature of atomic bonding? The physics in the nucleus do not allow the electron cloud to be compressed into the nucleus, so there is already a buffer that could be elastic i think.

[Jack]

The physics in the nucleus do not allow the electron cloud to be compressed into the nucleus, so there is already a buffer that could be elastic i think.

Ummm, yeah, OK...I'm sure you're right. :eek:

(Hey, I got a mental hernia just trying to understand the quote I provided.)

[Morgan_Freeman]

The speed of sound in any medium cannot exceed the speed of light.

So.. to be infinitely inelastic, the object would have to be infinitely small.

[Prometheus]

But if we could find the smallest cinstituant of matter (quark, gluon. meson - whatever the current smallest one is supposed to be), wouldn't it have to be perfectly dense?

But of course then it would be infinitely heavy, which we know isn't the case. But on some level can;t you find "pure" matter? And wouldn't i be perfectly solid and innelastic?

[Starboy]

Quote by: Prometheus Any thoughts?

I'm not sure that the concept of a rigid rod makes any sense in a relativistic context.

Starboy

[Morgan_Freeman]

Quote by: Prometheus But if we could find the smallest cinstituant of matter (quark, gluon. meson - whatever the current smallest one is supposed to be), wouldn't it have to be perfectly dense? But of course then it would be infinitely heavy, which we know isn't the case. But on some level can;t you find "pure" matter? And wouldn't i be perfectly solid and innelastic?

I guess "pure matter" would be a single atom. As far as I know, a single atom is perfectly inelastic. More likely, though, on that scale, classic mechanical concepts such as "elasticity" become moot.

[Prometheus]

Maybe not. I am not well versed on which points in newtonian/reletavistic/quantum physics cross over. It's seems prettty simple logic though.

[Prometheus]

Quote by: Morgan_Freeman I guess "pure matter" would be a single atom. As far as I know, a single atom is perfectly inelastic. More likely, though, on that scale, classic mechanical concepts such as "elasticity" become moot.

An atom is certainly elastic. The electrons can move away and toward the nucleus. You can compress it.

[Morgan_Freeman]

I know electrons occupy different energy states which correspond to different distances from the nucleus, but are you sure you can actually compress it?

[Starboy]

Quote by: Morgan_Freeman I know electrons occupy different energy states which correspond to different distances from the nucleus, but are you sure you can actually compress it?

Sure. It is done all the time. That is how you turn peanut butter into diamonds.

Starboy

[Prometheus]

I don;t know about the nucleus compressing, but the electrons move so as to make the volumne of the atom smaller. When the force is released, it goes back to it's normal size. Isn;t this elasticity on the atomic level?

As far as elasticity on the nucleic level, I have no idea.

[Starboy]

Here is a link to a paper that appears to deal with the problems realated to the concept of a rigid rod in SR.

http://panda.unm.edu/Courses/finley/...pers/jesse.pdf

Starboy

[Morgan_Freeman]

A quick survey tells me you're right. But my understanding is that on the sub-atmomic level, the whole concept of "matter" breaks down.

[Morgan_Freeman]

Good article, Starboy.

The next logical step is to consider the case where v is positive. This makes things even more inconsistent with reality. For this case, the “wave” is traveling in the opposite direction, starting at the end where the force was not applied, and ending at the end where it was applied. This means that the end where the force is applied will accelerate after the other end starts to accelerate. The wave travels from x=L to x=0. This obviously cannot be.

There you have it.

[tman_ndsu08]

Quote by: Prometheus But on some level can;t you find "pure" matter?

http://en.wikipedia.org/wiki/Superstring

[northtexan]

Quote by: Morgan_Freeman I know electrons occupy different energy states which correspond to different distances from the nucleus, but are you sure you can actually compress it?

Neutron stars. Beyond them, black holes.