How long would it take to move a pole one light year long one foot?

[Bender711]

A pole one light year long...

laying in bed last night I had this question pop into my pointy little head.

If I had a pole one light year long sitting between points A and B and I pushed it forward one foot from point A toward point B how long would it take to move at point B?


I've got an answer, but I'll wait to see what the people smarter than me have to say.

 

[russ_watters]

That's a meaningless answer, funker, since no such thing exists.

Bender, it the impulse would travel at the speed of sound in that material. For example, if the pole were steel, with a speed of sound of 4500m/s, it would take 6700 years for the impulse to reach the other end of the pole.

 

[ranger]

it would be instantaneous, provided a rigid body system

Err, please don't answer like that. You are proposing faster than light communication here. If it were instantaneous, then we could send morse (poking) instantaneously, whereas light would take one year. If you hit one end of stick with a hammer, would the other end hear it instantaneously? No. You must think of the interaction at a molecular level.

EDIT: Russ beat me to it.

 

[russ_watters]

Huh? No, minijumbuk. You are simply wrong. Force has to be transmitted via molecular interactions. If forces propagated instantaneously, there'd be no sound because objects wouldn't oscillate. Striking a large bell with a hammer would just make it swing back and forth.

Gravity is different, but it still propagates at the speed of light.

 

[Integral]

I have deleted some blatentely incorrect posts.

Locking since the question has been answered and there is no point in further discussion.