Comment on The Planet, some string and a bell.
NeoNachtwaechter@lemmy.world 8 months agoJust for fun: Assuming the motion of the string travels at the speed of sound (I have no idea if it actually would, it just sounds right)
It is true in principle. But the speed of sound is different, depending on the material. For that string we can assume it to be roughly 10 times faster than in the air.
would be about 10.5 hours between you pulling the string and the bell ringing
~ 1 hour then.
piecar@lemm.ee 8 months ago
Wouldn’t the motion of the string move at the speed of the pull!? Assuming no compression.
NeoNachtwaechter@lemmy.world 8 months ago
Compression and expansion is real. The first part of the string moves with your hand, at the same speed as your hand moves. But then it takes some time until further parts of the string - or the final part of the string - even start with their motion. Ok? And here we were talking about how fast this “beginning of the motion” travels forward through the string. That’s the speed of sound.
TheActualDevil@lemmy.world 8 months ago
Okay, but what if there is no compression or expansion? What if it’s a rigid string already stretched out just enough to be expanded completely but not enough to move the bell? Or maybe a thin wire of the same weight?
Zippy@lemmy.world 8 months ago
Physics. The force you place on that string will effect the far end only at a rate no sooner than the speed of sound thru said medium.
The speed of sound in metal is about 17000 feet per second. Of materials on earth it has some of the fastest rates of transfer. But if you had a metal rod 17000 feet long and pushed one end a foot, the other end wouldn’t move a foot till a second later. It will compress.
Interestingly a neutron star has material that is so densely compacted that the speed of sound thru that material is approaching that of the speed of light.
NeoNachtwaechter@lemmy.world 8 months ago
That means, the speed of sound is infinite in your material. It doesn’t happen in this world.