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IAmNorRealTakeYourMeds@lemmy.world ⁨4⁩ ⁨hours⁩ ago

Fuck it, question that I had since 10 years old.

if I have a very long stick, and I flick it. what would happen to the tip? what if a laser pointer is used? at a certain distance, the beam would be moving (sideways) faster than light.

it might work better with a whip rather than a solid stick.

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skisnow@lemmy.ca ⁨4⁩ ⁨hours⁩ ago
The end of the stick would respond at the speed of sound travelling through the medium of a stick.

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- IAmNorRealTakeYourMeds@lemmy.world ⁨49⁩ ⁨minutes⁩ ago
  but how will it look like?
  
  for a short scale it’ll be a straight line. but a few light years away? where the abstract dot is moving faster than the speed of light? what shape would you see? definitely not a straight line. and definitely some time issues. like it’ll hit you and then you’ll see it hit other planets you’re left and right?
  
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- Korhaka@sopuli.xyz ⁨3⁩ ⁨hours⁩ ago
  Now I wish I had a nice big wall about a light second away and a massive laser to draw things on it.
  
  Bonus: angle the wall so that the left side is a light second and the right side is a light minute away. Alternate the laser on/off.
  
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midribbon_action@lemmy.blahaj.zone ⁨3⁩ ⁨hours⁩ ago
First question: two reasons that wouldn’t work: the stick would just break, obviously, but if it was a super duper stick, the torque required to accelerate the end past the speed of light is directly related to how long the stick is, so any increase in speed from a longer stick will be offset by the need to apply more force at your end. Therefore the energy required to flick a stick to the speed of light does not depend on the length of the stick, you are simply creating a reverse lever of sorts. It’s still an infinite energy requirement, assuming the stick has mass.

The second question is a lot easier. The light is traveling directly away from you at all times, there is no sideways motion.

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- sneezycat@sopuli.xyz ⁨3⁩ ⁨hours⁩ ago
  It’s actually simpler: the stick will deform because whatever movement you do travels at the speed of sound of the material the stick is made out of.
  
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  - midribbon_action@lemmy.blahaj.zone ⁨3⁩ ⁨hours⁩ ago
    Why does it matter how long it takes for the torque to travel down the stick? The question was about the speed of the tip in the orbital direction, not the speed of the wave in the radial direction outward.
    
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    sneezycat@sopuli.xyz ⁨3⁩ ⁨hours⁩ ago
    I see your point. Still, it shows there’s no such thing as a “super duper stick” because there’d be shearing forces pulling the atoms apart faster than they can move together.
    
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Brkdncr@lemmy.world ⁨3⁩ ⁨hours⁩ ago
That’s where things get weird. The tip won’t exceed the speed of light. You could have a section near you moving at the speed of light and the tip will also be moving at c, because c is the limit.

If you were on a train moving at 100mph, and threw a baseball at 50mph in the direction of travel, then the baseball is moving at 150mph. But if you were moving at c and threw that baseball it would not go faster than c.

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- Duke_Nukem_1990@feddit.org ⁨2⁩ ⁨hours⁩ ago
  In fact, everything would move very very rapidly away from the baseball hitting the first air molecule it touches (assuming you yourself have no mass in this scenario).
  
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spicehoarder@lemmy.zip ⁨2⁩ ⁨hours⁩ ago
The Information that the stick has begun to move takes time to travel through the stick. Kind of like bending, but not really.

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