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Re: [Phys-l] velocity-dependent mass (or not)



I interspersed a few comments...

Spinozalens@aol.com wrote:
In a message dated 6/30/2009 9:55:41 AM Eastern Daylight Time, maddox@physics.Auburn.EDU writes:

From: WC Maddox

Relativistic mass just won't go away. In the article by Gary Oas (On the abuse and use of relativistic mass) arguing against the use of relativistic mass there is a question that students were asked. It amounts to weighing yourself on a spring scale at rest with respect to the Earth and then weighing yourself using the same scale while moving relative to the Earth. Would you, at least in principle, detect a change in the scale reading? The answer in the article was no on the grounds that mass does not increase with velocity.
***
Earth referenced scales are not inertial - so it is easy (??) to move with respect to
the Earth so as to fix the Sun height and register an increased weight.
Oh, was I supposed to recognize I was in a Physicist's conception of Earth? :-)
In an article by Bernhard Rothenstein (Relativistic velocity transformation as a genitor of transformation equations) there is a setup involving a two pan balance. The pans are on those frictionless rods found in introductory physics texts. There are given equal speeds (V) in opposite directions. At time t (center observer time) equal masses are placed on the pans which are equal distances from the center. The apparatus will remain balanced from the point of view of an observer in the center. What about from the point of view of an observer (A) traveling with one of the masses? According to the article, if A uses the relativistic velocity addition formula to calculate the speed of the other mass (B) and uses this to find the length of arm B, then observer A finds arm B is shorter than arm A. According to the article A finds that B is moving from the center with a speed less than V so distance traveled by B is less than distance traveled by A. To remain balanced, mass B would have to be larger by an amount given by the relativistic mass formula.
In terms of observables, this seems to be an acceptable story to use in
connection with the hypothetical....
Did one author make a mistake? Does it matter whether it is a spring balance or a two pan balance? Are both authors wrong by not bringing in general relativity?

End Message
Ah, there's the rub: I can only answer - don't know. Should I care?




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Measurements in your own frame (absent acceleration) produces the same results regardless of what an observer in a different inertial frame measures your velocity relative to him to be. While he sees your clock running slower, to you nothing has changed.
Bob Zannelli
This seems to have the ring of accepted wisdom. Has it, in fact?