4 ms·
If you imagine a pipe filled with marbles and you add a marble to one end, a marble will pop out the other end instantaneously (i.e. the speed of light).
by viggity 11y ago
If you imagine a pipe filled with marbles and you add a marble to one end, a marble will pop out the other end instantaneously (i.e. the speed of light).
- cmiller1 11y agoA fun little caveat of that fact is that if you were able to make a 100% incompressible material you would violate causality. If the glass in your marbles did not compress at all then the "information" that you inserted your marble would reach the other end before it actually happened (faster than the speed of light)
- deleted 11y ago[deleted]
- gipp 11y agoActually, that particular hypothetical would happen at the speed of sound in marbles (plus some corrective factors due to the interfaces between the individual marbles). But your intuition about propagation vs drift velocity is correct.
- lfowles 11y agoCould you expand more on why it's the speed of sound?
- Geee 11y agoIf you touch a marble at the other end, you will feel the vibration at the other end with the delay equal to the speed of sound (and also hear the vibration when it's transferred to air). The speed of sound is the propagation speed of mechanical energy in a matter.
- mikeash 11y agoThe speed of sound is the speed at which any disturbance in the material propagates. When you push on a marble, that's a disturbance. The other end of the marble begins to move when the disturbance reaches that end. In this scenario, the disturbance is then transmitted to the next marble, and so on in that fashion, all at the speed of sound.
- Sharlin 11y agoA mechanical impulse travels through a solid via atoms literally pushing and pulling each other. Pushing something is a mechanical impulse; sound is a series of mechanical impulses. The propagation speed is the same because they are the same thing.
- fineman 11y agoPerhaps it's simpler to think of the other way - why the speed of sound is in marbles is the same as the speed that a marble would pop out of the tube when another was inserted. Imagine that instead of pushing a whole marble in you merely wiggled the last one rapidly.
- viggity 11y agoI was suspicious of your answer, but the second answer here: http://physics.stackexchange.com/questions/2175/is-it-possible-for-information-to-be-transmitted-faster-than-light-by-using-a-ri?newreg=74bcd6368e374e53b223ca1640321711 http://physics.stackexchange.com/questions/2175/is-it-possib... seems to show that you're right.
- viggity 11y agoI was suspicious of the speed of sound thing, but this looks to back that assertion up. http://physics.stackexchange.com/a/4730/81783 http://physics.stackexchange.com/a/4730/81783