Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Oscar Tucker on 22/11/2011 02:01:03

Title: How fast would force travel?
Post by: Oscar Tucker on 22/11/2011 02:01:03
Oscar Tucker  asked the Naked Scientists:
   
Hi,

All the recent talk of neutrinos has got me wondering something (assuming relativity is true). If you take a really long tube and fill it completely full of rigid balls, then put another ball in the end, will one come out the other end instantly or will there be a speed of light delay? Also, is there any way to send messages faster than light?


Many Thanks

Oscar Tucker, a student from Wales. 

What do you think?
Title: How fast would force travel?
Post by: Phractality on 22/11/2011 05:33:47
A pressure wave in a solid propagates at the speed of sound  (http://en.wikipedia.org/wiki/Speed_of_sound#Speed_of_sound_in_solids) for that solid. For steel, it's about 6 km/s; for solid kevlar, it's about 8 km/s.

The speed of light is about 300,000 km/s.
Title: How fast would force travel?
Post by: syhprum on 22/11/2011 06:21:02
On old railway signaling systems where signals were operated some way away via long steel bars the relativly slow speed of the pressure wave in the bars was quite apparent.
Title: How fast would force travel?
Post by: Geezer on 22/11/2011 08:58:37
Quote from: syhprum on 22/11/2011 06:21:02
On old railway signaling systems where signals were operated some way away via long steel bars the relativly slow speed of the pressure wave in the bars was quite apparent.

Ahem! Did somebody mention "railways"?

Actually it was the points (switches) that were operated by long steel bars. The signals were operated by pulling on a piece of wire against a weight at the signal. If the wire broke, the signal was supposed to fail to the "stop" position (except that with some types of signals, snow or ice might cause a signal to remain in the "go" position.)
Title: How fast would force travel?
Post by: syhprum on 22/11/2011 09:39:14
The same effect would be noticed pulling the wire no doubt.
As for signaling faster than the speed of light it has been suggested that gravity waves move faster than light but they are very weak and you would have to shove black holes around to generate any reasonable amount of power. 
Title: How fast would force travel?
Post by: imatfaal on 22/11/2011 12:19:12
Quote from: syhprum on 22/11/2011 09:39:14
The same effect would be noticed pulling the wire no doubt.
As for signaling faster than the speed of light it has been suggested that gravity waves move faster than light but they are very weak and you would have to shove black holes around to generate any reasonable amount of power. 


Mainstream view which comes from general relativity is that gravitational waves propagate at the speed of light not above it.  This is yet to be experimentally verified - but that is being attempted