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How does mass increase when you approach the speed of light?

This question addresses Einstein's theory of Special Relativity. If my answer does not satisfy you, there are many clear books on the topic in any university bookstore. When a particle/object travels close to the speed of light, and is thus considered "relativistic", the energy of the particle is expressed as E = (gamma)*mass*velocity. Here gamma is a relativistic factor that is greater than unity. So, one could consider the factor (gamma)*mass a new mass, one that is larger than the mass of the particle when it is at rest. This is why you hear that mass increases when you approach the speed of light. It can be argued that it is only an appearance of greater mass, or that it depends on how you look at the problem. In short, it is all relative. ;) It should be noted, however, that in order for an object to actually reach the speed of light, it must have no mass, since E=mass*speed of light^2. This is true of massless particles such as the photon, the "particle" that transports light. (Notation:* means multiply by and ^2 means squared).

robin d erbacher

I apologize for being picky, but in the last response, I think that should be the "momentum" = gamma*mass*velocity.

timo p grayson

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