It's a nice quantity to talk about, because it will be the same for all particles of a given type, regardless of their energy. Since potentials can be arbitrarily defined, this would seem to make the mass of particle arbitrary as well. The trick here is that potential energy is not a property of the particle. Imagine an electron moving through a magnetic field. If you suddenly turn off the magnet, the potential energy is changed, but nothing about the particle has been altered.
Potential energy is in fact a property of the field .
As a particle rises, its mass and kinetic energy are unchanged, but energy is stored in the gravitational field. Should it fall, that energy is transferred to the particle in the form of kinetic energy, and mass increases. Copyright 1998-1999, Room103 group. Don't steal this. All rights reserved.