Relativistic Density - Check My Work & Learn Methods

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The discussion revolves around calculating the relativistic density of a cube moving at 0.95c, with initial confusion over the application of length contraction and mass changes. Participants clarify that only the dimension parallel to the motion experiences length contraction, while mass increases due to relativistic effects. The correct approach involves using the formulas for relativistic mass and length contraction, leading to a new density calculation. Ultimately, a density of approximately 20.5 kg/m^3 is suggested as the correct answer, emphasizing that the density must increase due to the effects of relativistic motion. The conversation highlights the importance of understanding the underlying physics principles in these calculations.
  • #31
I think @PeroK and myself are on the same page here. If you perceive a conflict, either of us can probably clarify it away.
 
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  • #32
Okay thank you!
 
  • #33
jbriggs444 said:
I think @PeroK and myself are on the same page here. If you perceive a conflict, either of us can probably clarify it away.

Yes, I agree.

I was distracted trying to find a way to show that it's true in general, even when motion is not in the same direction as one side of the cube. Which I've just spotted!
 
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  • #34
PeroK said:
I was distracted trying to find a clever way to show that it's true in general, even when motion is not in the same direction as one side of the cube. Which I've just spotted!
I was taking it as an obvious geometric property -- scale down one dimension by a factor of ##\gamma## and the volume clearly goes down proportionately.

I gave a moment's though to Terrell rotation, but it does not apply.
 
  • #35
jbriggs444 said:
I was taking it as an obvious geometric property -- scale down one dimension by a factor of ##\gamma## and the volume clearly goes down proportionately.

Yes, I was only thinking about cubes, parallelopipeds and the triple scalar product! Then, I realized ...

o:)
 

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