# Speed of Light Thought Experiment

1. May 1, 2010

### Spoink

What would happen if you were to construct a massively lengthy object (Suppress your inner perv for a moment please) and rotated it so that the part of the object farthest away from you would theoretically move faster than light?

2. May 1, 2010

### Integral

Staff Emeritus
This is a very common misconception frequently brought up here. Any information concerning the motion of end A is transmitted to end B at the speed of sound in the material. If you make an effort, say with a sledge hammer, to move the stick at a speed faster then sound in the material you will simply deform the end while the vibrations created will travel away at the speed of sound.

BTW, the speed of sound in materials is MUCH smaller then the speed of light.

3. May 1, 2010

### Staff: Mentor

...For rotating objects, you'll find that the torque required to get it to rotate keeps increasing as the rotational speed increases, and you'll never get to C. It's the rotational equivalent of the linear speed 'barrier'.

4. May 1, 2010

### Staff: Mentor

Also the material stress in the rod becomes infinite.

5. May 1, 2010

### Integral

Staff Emeritus
Ok, so we attempt to spin a long rod. If the rod is not rigid then if we push the short end to hard the longer end will not stay straight but will bend. This leads me to the conclusion that the far end of any rod will not move at the same time as the short end. I well bet (with no real proof) that the wave of information moving to the far end of the rod will travel at the speed of sound in the rod. If you attempt to accelerate the short end faster then some value determined by the material the rod will either deform or break.

example, http://www.physicscentral.com/experiment/physicsathome/images/towers-falling.jpg" [Broken]

Last edited by a moderator: May 4, 2017
6. May 1, 2010

### Spoink

Thanks for the answers. I'm not incredibly well read but am steadily learning and hopefully such misconceptions will be erased from my world view as I gather more knowledge. :)