It can look dumb, but I always had this question as a kid, what physical principles would prevent this?
this post was submitted on 11 Feb 2025
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The problem is that when you push an object, the push happens at the speed of sound in that object. It's very fast but not anywhere near the speed of light. If you tapped one end of the stick, you would hear it on the moon after the wave had traveled the distance.
For example, the speed of sound in wood is around 3,300 m/s so 384,400/3,300 ~= 32.36 hours to see the pole move on the moon after you tap it on earth.
Your math is off. The Moon is about 384,400 KILOmeters from the Earth, not meters. So 116,485 seconds, or a bit over 32 hours.
Oh right. I'll edit my comment
I swear I've seen a video of someone timing the speed of pushing a very long pole to prove this very thing. If I can find it I'll post it here.
*Found it! https://www.youtube.com/watch?v=DqhXsEgLMJ0 I can't speak to the rigorousness of the experiment, but I remember finding it enlightening.
AlphaPhoenix is definitely one of the best scientists on YouTube, that video is good.
Cool vid, thanks for sharing
Damn, so that means no FTL communication for now... ๐
Hear me out... What about a metal stick?
Metal is a lot heavier than wood. You'd never be able to lift it to the moon.
But can you lift it from the moon? Gravity is a lot lower there.
Large if factual
You should make it out of feathers. Steel is heavier than feathers.
NASA: "Hold my beaker."
What if you had a crane?
Or a duck.
Or hope
๐ค
For now
13 hours later Now?
Hold on, let me check. I don't think so
Wow, TIL that the speed of sound has this equivalence
It's also why rocket nozzles can't be infinitely thin :)
I don't get it. Care to explain?
Does that mean the theoretical speed limit for a jet aircraft is how fast sound propagates through the airframe?
No, a jet aircraft moves by pushing air behind it, the theoretical limit would have to be somehow related to that
XKCD has alot of thought experiments like this.
The theoretical limit could be related to either of those things; it just depends which is lower.
(It's almost certainly the one you mentioned.)
Exactly