this post was submitted on 11 Feb 2025
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It can look dumb, but I always had this question as a kid, what physical principles would prevent this?

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[โ€“] [email protected] 234 points 2 days ago* (last edited 2 days ago) (29 children)

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.

[โ€“] Tarqon 2 points 2 days ago (1 children)

Does that mean the theoretical speed limit for a jet aircraft is how fast sound propagates through the airframe?

[โ€“] [email protected] 6 points 2 days ago (2 children)

No, a jet aircraft moves by pushing air behind it, the theoretical limit would have to be somehow related to that

[โ€“] untorquer 2 points 2 days ago

XKCD has alot of thought experiments like this.

[โ€“] grue 1 points 1 day ago

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.)

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