Faster than light: Instantaneous lever

  • #1
ISamson
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Hello.
I have been thinking on faster than light things. I thought about: chemical engines, lasers, wormholes... All that kind of cool, advanced physics.
But, I stumbled on faster than light mechanical actions. I thought about a lever: first class, if you wish, if you apply a force to one side, then something instantaneously occurs on the 'load' side of the lever. This change in speed, direction is instantaneous, which is faster than light, right?
Could this be used in travel?
Please don't judge me on my weekend-wonders.
 

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  • #2
A.T.
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if you apply a force to one side, then something instantaneously occurs on the 'load' side of the lever.
No, it travels at the speed of sound in the lever.
 
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  • #3
sophiecentaur
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A lever would be solid. Movement propagates through real objects at the speed of sound (only) through an object.
(Beat me to it!!!)
 
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  • #4
ISamson
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No, it travels at the speed of sound in the lever.
Movement propagates through real objects at the speed of sound (only) through an object.
Sound.
I didn't know that! Why? I always thought it would be instantaneous.
 
  • #5
FactChecker
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Sound.
I didn't know that! Why? I always thought it would be instantaneous.
Because both sound and force travels by means of molecule-to-molecule interaction, each interaction taking a tiny bit of time. And there can be a lot of molecules from one end of a lever to another. It is not instantaneous.
 
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  • #6
sophiecentaur
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“Sound” is just a general term for any disturbance. The atoms are displaced as the lever is moved and they push-pull nearby atoms. Any material will deform and that takes time. Hence the finite time to propagate sound or a twist.
 
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  • #7
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Sound.
I didn't know that! Why? I always thought it would be instantaneous.
The speed of sound in a material is defined as the speed at which mechanical changes propagate in that material. It happens at that speed because that is how that speed is defined
 
  • #8
jbriggs444
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The speed of sound in a material is defined as the speed at which mechanical changes propagate in that material. It happens at that speed because that is how that speed is defined
In a fluid like air, it is easy to define a "speed of sound" because the disturbance that propagates is always a compression wave. The properties of the fluid, specifically its density and its compressibility, allow one to calculate that speed from first principles. Or one can measure it with a starter's pistol, a stopwatch and a wall.

In a solid like steel there are two different types of disturbance that can propagate. You can bang a hammer on the end of a steel rod and see how long it takes before a microphone at the other end picks up the compression wave. Or you can try to swing it like a bat and see how long it is before the resulting "shear wave" reaches the far end so that the end starts to move. The speed of a compression wave depends on the compressibility of the steel -- its bulk modulus. The speed of a shear wave depends on its lateral stiffness -- its shear modulus.
 
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  • #9
berkeman
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  • #10
russ_watters
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You can bang a hammer on the end of a steel rod and see how long it takes before a microphone at the other end picks up the compression wave.
And this experiment has been done, I think by a member of this forum. And it would also make a good basis for a high school science fair project.
 
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  • #11
Vanadium 50
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Please don't judge me on my weekend-wonders.
Fair enough, but I think it's also fair to criticize you for the title, where you claim that you have found something that a century of professional physicists did not - merely by "weekend-wondering".

I didn't know that! Why?
I would think about it from the other direction than most responses. If x is the speed that a mechanical disturbance propagates, what is the relationship between x and something we call "the speed of sound" (which is a kind of mechanical disturbance). i.e. don't get too caught up in the word "sound".
 
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  • #13
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"Weekend wondering"? We have to be careful about how we criticize insights. Einstein's insights didn't occur in a research lab after years of painstaking experimentation. The ideas came as insights, flashes of genius, that then took years of painstaking work to flesh out. Human creativity is a nebulous process. Many of the greatest tech companies originated in garages where the founders had some pretty "wild" insights which certainly could have been Weekend Wonderings. Often the level of pure creativity in those austere places equaled or exceeded what was done in the multi-billion dollar research labs. If only creative insight could be legislated by aggressive managers, we'd have a lot of really great insights. Unfortunately, we can't drive when or where the creative insight will come, and the harder we try and drive it, the greater the possibility that nothing will result. What we can do is be aware when those insights come, we have to act on them.
 
  • #14
berkeman
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"Weekend wondering"? We have to be careful about how we criticize insights. Einstein's insights didn't occur in a research lab after years of painstaking experimentation. The ideas came as insights, flashes of genius, that then took years of painstaking work to flesh out. Human creativity is a nebulous process. Many of the greatest tech companies originated in garages where the founders had some pretty "wild" insights which certainly could have been Weekend Wonderings. Often the level of pure creativity in those austere places equaled or exceeded what was done in the multi-billion dollar research labs. If only creative insight could be legislated by aggressive managers, we'd have a lot of really great insights. Unfortunately, we can't drive when or where the creative insight will come, and the harder we try and drive it, the greater the possibility that nothing will result. What we can do is be aware when those insights come, we have to act on them.
Except, the successful examples that you mention of insights and invention have an important difference from the weekend wonderings of some folks based on pop-science and YouTube videos they have watched. If you want to discuss that difference, you should probably start a different thread, since it would be off-topic for this thread. :smile:
 
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  • #15
russ_watters
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The question is adequately answered, so I think this is a good place to close the thread.
 
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