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Talk:Theory of relativity (view source)
Revision as of 05:19, December 2, 2009
, 05:19, December 2, 2009→orthogonal force: new section
::::::Thanks for the reference, Jacob... <quickly read old discussion...> Okay, it seems that the consensus there was to omit the section entirely. However, it seems to have come back in as the first paragraph in "Political aspects". I can see arguments for either including or excluding it. As for whether to include Einstein's opinion - good point, Andy. I reread the current page, and on second look, it doesn't seem to be as bad as [[user:jfraatz|Johanan Raatz]] seems to think. --[[User:EvanW|EvanW]] 15:57, 29 November 2009 (EST)
::::::Thanks for the reference, Jacob... <quickly read old discussion...> Okay, it seems that the consensus there was to omit the section entirely. However, it seems to have come back in as the first paragraph in "Political aspects". I can see arguments for either including or excluding it. As for whether to include Einstein's opinion - good point, Andy. I reread the current page, and on second look, it doesn't seem to be as bad as [[user:jfraatz|Johanan Raatz]] seems to think. --[[User:EvanW|EvanW]] 15:57, 29 November 2009 (EST)
== orthogonal force ==
ASchlafly and Jfraatz seem to have been talking past each other on the subject of what happens when a force is applied orthogonally vs. longitudinally to a relativistic particle. There is no need for the acrimony here, and there is no need for arguing over the significance of mass being a scalar rather than a vector.
The right way to analyze problems involving force and acceleration is with the "4-velocity", "4-acceleration", "4-momentum", and "4-force". These are the modern concepts that people use. The 4-velocity is a vector in spacetime. It is always a unit vector; it just "tilts" when a particle moves. The 4-momentum is the 4-velocity times the mass. That's the "rest mass". The notion of "relativistic mass" is old-fashioned. The right way to think about it is that the momentum increases faster than mv, doing so ''as if'' the mass had gone up. But it's better to think of the mass as staying the same, and the formula for momentum being <math>mv\gamma</math> rather than just mv.
The 4-acceleration is the rate of change in the 4-velocity, as measured by the proper time, and the 4-force is the rate of change of 4-velocity. Conservation of momentum applies, and says that 4-forces cancel, same as in Newton's laws. So you can find the deflection of a particle, correct for relativity, by checking conservation of momentum.
This stuff is treated in modern physics textbooks, such as Halliday and Resnick.
[[User:SaraT|SaraT]] 00:19, 2 December 2009 (EST)