What Happens When a Rod Is Pushed Beyond Its Signal Propagation Speed?

[Zhivago]

Hello everyone, this is my first thread :)

It all started from the perfectly rigid rod connected from Earth to the moon and how fast the signal would get there if I pushed it. I understand the signal can't get there instantaneously because the inner structure of the atoms of the rod has a propagating limit.

But what happens if I push a rod (can be a regular sized one) with an energy high enough to give the first atoms in one end of the rod a speed greater then the propagating speed in the rod?
My answer would be: the rod would want to deform itself, or the energy would be converted to heat / radiation.
But I'm not quite sure of any of these... What do you think?

 

[rcgldr]

The limiting factor is the speed of sound in the rod. If you impart an impulse faster than the rods speed of sound, it's similar to the air. The result is a shock wave that travels at the speed of sound, which dissipates into a normal sound wave over distance and time, although I'm not sure of the rate of disspation, espeically in the case of a very long rod.

A bit off topic, but in the air, shock waves sould like a crack, not a boom. You have to be far enough away from the source of the shock wave for it to dissipate and turn into a normal sound wave in order to hear the boom.

Assuming the rod is conductive, the speed of electrical propagtion is much faster than the speed of sound in a rod.

 

[sir-pinski]

Hello and welcome to the forum! It's great to have you here.

In response to your question, the propagation of a signal in a rod is a complex process that involves the transfer of energy and information through the material. It is true that the signal cannot travel instantaneously due to the limitations of the inner structure of the atoms in the rod.

If you were to push the rod with a high enough energy to exceed the propagating speed in the rod, there are a few possible outcomes. One possibility is that the rod would indeed deform itself in an attempt to accommodate the energy and movement of the atoms at the end being pushed. This could result in the rod bending or even breaking if the force is strong enough.

Another possibility is that the excess energy would be converted into heat or radiation, as you mentioned. This is because when atoms are pushed beyond their normal speed, they can release energy in the form of heat or radiation as a way to balance out the excess energy.

It's also important to consider the properties of the material the rod is made of. For example, a metal rod may be more rigid and able to withstand higher forces, while a plastic rod may deform more easily.

Overall, it's difficult to say exactly what would happen without knowing more specific details about the rod and the force being applied. But it's safe to say that the rod would likely experience some kind of deformation or energy conversion if pushed with enough force to exceed the propagating speed. I hope this helps answer your question!