- Apr 2008
- On the dance floor, baby!
Then you'd better check again. As benit13 said nothing changes the rest mass of a particle. It is the mass of a particle with no regard to motion. Now, when you heat something up then the particle's kinetic energy increases and the particles gain momentum. The total energy of the particle then obeys \(\displaystyle E^2 = (pc)^2 + (mc^2)^2\), where we are using whatever average p is appropriate. But m is the rest mass and does not change under any circumstances, even when changing reference frames. Now, if we are talking about a macroscopic object its rest mass due to the individual particles stays the same, so we still get the same rest mass. What happens is the mass of the whole object reflects the extra kinetic energy contained in it. This does change the mass of the object, but not it's rest mass. The thermal energy simply gets absorbed into its total energy."The special-relativistic thermodynamics is an interesting area which has not been settled to full satisfaction AFAIK but nonetheless, it should be pointed out that when you heat up a body, the individual particles of the body only gain kinetic energy--so the rest mass of the individual particles does not change. But when you see the body as a whole with its center of mass at rest (and whose constituent particles are only engaging in thermal motion), the rest mass of the full body as a whole gets increased, in particular, the heat you provide goes into the rest mass of the body as a whole"
This is exactly, what I predicted