Exploring the Physics of Pushing Objects Relativistically

  • Thread starter Jonathan
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In summary, when you push on an object and accelerate it to some relativistically small velocity, does the impluse from your push travel through that object as a longitudinal pressure wave at the speed of sound? It seems like that should be true, but that also implies that the object should contract slightly and that one end of the object would attain the 1 m/s velocity before the other end does, (assuming that the object is long enough that one can reach this velocity before the pressure wave meets the other end) and for some reason I don't like that conclusion, even though it makes sense.
  • #1
Jonathan
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When you push on an object and accelerate it to some relativistically (so we can really, really ignore lorentz contraction) small velocity (say a nice 1 m/s), does the impluse from your push travel through that object as a longitudinal pressure wave at the speed of sound (what ever that may be for that object)? It seems like that should be true, but that also implies that the object should contract slightly and that one end of the object would attain the 1 m/s velocity before the other end does, (assuming that the object is long enough that one can reach this velocity before the pressure wave meets the other end) and for some reason I don't like that conclusion, even though it makes sense.
 
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  • #2
Perhaps your post would make sense if you explained WHY you don't like the idea of pressure waves in solids.
 
  • #3
Learn to like that conclusion. This falls in line with something I just posted in the thread entitled 'energy absorption'. Consider a steel rod that is about 5 to 10 feet long. Hit it with a hammer from one end. The 'shock wave' will arrive at the other end a short time later. The 'shock wave' is basically the far end being moved by the hammer only at a later time. So yes, there is a speed of push so to speak.
 
  • #4
There isn't anything about solids that special and makes them not compressible. Metals are actually very close to perfectly elastic for small displacements.

Your conclusion is correct.
 
  • #5
That's what I thought; HallsofIvy: What I don't like is that one end will move before the other. It feels to me like macroscopic quantum superpostion, ie two places, one time, one object. (I knows that that's unrelated, it just feels as weird as that would.) It's like one of Zeno's paradoxes or something.
 
  • #6
Originally posted by Jonathan
That's what I thought; HallsofIvy: What I don't like is that one end will move before the other. It feels to me like macroscopic quantum superpostion, ie two places, one time, one object. (I knows that that's unrelated, it just feels as weird as that would.) It's like one of Zeno's paradoxes or something.

Read my post in 'energy absorption'. If both ends moved at the same time then an object could be used for faster than light signaling. It's not permitted.
 
  • #7
Another way to consider your objection, what would happen to sound in a solid if there weren't pressure waves moving around in there? Heck, how would an earthquake work (would the whole Earth shake?)?

Some things in science don't make sense when you look at them from one direction, but if you look at them from another direction, they make a lot more sense.
 

1. How does pushing an object at relativistic speeds affect its mass?

According to Einstein's theory of relativity, as an object approaches the speed of light, its mass increases exponentially. This means that the object will become heavier and require more force to accelerate it further.

2. Can an object be pushed faster than the speed of light?

No, according to Einstein's theory of relativity, the speed of light is the maximum speed at which anything in the universe can travel. Therefore, it is impossible to push an object faster than the speed of light.

3. How does pushing an object at relativistic speeds affect its length?

Similar to the effect on mass, an object's length also changes as it approaches the speed of light. The length of the object will appear to decrease in the direction of motion, a phenomenon known as length contraction.

4. What is the relationship between force and acceleration when pushing an object relativistically?

As an object's velocity approaches the speed of light, the relationship between force and acceleration becomes less linear. This means that a larger amount of force is needed to produce a small increase in acceleration when an object is already moving at high speeds.

5. How does pushing an object at relativistic speeds affect time?

According to the theory of relativity, time slows down as an object approaches the speed of light. This means that a clock on the moving object will appear to tick slower than a stationary clock, and time will pass slower for the object than for an observer at rest.

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