Why does a particle gain mass/momentum as its velocity increases?
How does this happen?
Ignore the previous reply, it was wrong and crackpottery and got deleted accordingly.
It does not gain mass. It gains momentum as momentum is defined as a velocity-dependent quantity (in classical physics, just mass*velocity).
You must be referring to relativistic mass. The change in mass with speed is due to the combination of length contraction and time dilation, i.e. due to the properties of spacetime.
Momentum is directly proportional to mass of object as well as the velocity,
And thats why mass doesnt change but the velocity in your case may be constant or relative!
Thats actually the definition of momentum too.
As mfb said it doesnt gain mass but momentum.
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