Mass relation with velocity

[eburatti]

Question: If mass increases with speed, becoming infinite at c, then does it also follow that at speed of 0, would mass be 0? Now I'm talking about a mass at absolute zero, and velocity relative to (space/time?) of 0. Don't know how that could be accomplished - it's just a thought that's driving me crazy.

[Xyph]

Relativistic mass becomes infinite at c. Something at absolute zero with a velocity of 0 relative to an observer would have no relativistic mass. It would still have rest mass, though, which wouldn't change no matter what the velocity or temperature.

[qrasy]

There is no absolute frame of view, so "relative to space/time" is not well-defined.

 

Rest mass is defined as the mass measured when the thing is not moving (well, there is no absolute frame so we should choose a frame in which it rests), it never change with velocity. Apparent mass grows larger as the speed approaches s. Remember the velocity and apparent mass correspondence is not linear so having infinite apparent mass at v->c does not imply anything in v->0.

[LazerFazer]

Well, to answer this, we need to look at the mass-velocity equivalence formula (from special relativity):

 

m=m(rest)/(sqrt(1-(v^2)/(c^2)))

 

so, if v=0, then you get m=m(rest)/(sqrt(1))=m(rest).

 

And yes, as Xyph said, rest mass doesnt change ever, unless of course you chop off a body piece or something.

 

cheers,

LF