The speed of...

[RossGr]

Here is a good description of phonons in a material.

 

[MrDudeMan]

Originally posted by: Eeezee

Originally posted by: Calin
It will slow even when travelling thru air - and some particles can travel faster than light in air. I think this is called Cherenkov radiation, when you have protons flying thru air faster than speed of light in air (but NO faster than speed of light in a void).

There are relativistic effects that would otherwise make a particle seem to travel faster than the speed of light. For example, muons that form in the atmosphere can be detected on the surface. However, the detectable lifetime of these particles is incredibly short, and in order to be detectable on the surface it would have to get there with a speed that is greater than the speed of light in a vacuum. Luckily relativity comes along and shows that spacetime curves so that the muon shows up just fine while only moving near the speed of light.

you have the right idea, but that isnt entirely true. the muons do not have to apparently travel faster than C to be observed by a third party at a distance much greater than the proper length calculated by knowing the proper time. that is the genius of relativity - it makes it possible to observe such things without breaking the speed limit.

also, the optical tricks you speak of to speed up the apparent speed of light are things such as the earth moving into and out of the light path from the sun to the moon. the shadow on the moon can move faster than c due to the angle of incidence of the incoming light on the moons surface. it isnt so much a trick as it is geometry.

lastly, electrons in a wire move extremely slow unless you are dealing with very high currents, but even then they arent necessarily moving quickly. mm/s sounds about right for the average net movement.