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
NASA: "Hold my beaker."
What if you had a crane?
Or a duck.
Or hope
You should make it out of feathers. Steel is heavier than feathers.
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?
There are multiple forces at work in a converging rocket nozzle:
These two effectively cancel out, which is why the actual effect of making the nozzle thinner/converge is that it increases the back pressure within the engine (constricted space, smaller hole), essentially (idk how) increasing the efficiency of the fuel burning.
However, when the nozzle gets too thin, the exhaust becomes faster than its speed of sound. Since the pressure travels at the speed of sound, it can now not actually get back into the engine anymore. So that's the limit of how thin you can make the nozzle. The pressure has to get back into the engine to have its effect, so you can't make the exhaust travel faster than its speed of sound.
If any of this sounds wrong to anyone, let me know, I'm not an expert in this.
Exactly