Rest mass

Rest mass, which may also be referred to as invariant mass, intrinsic mass, proper mass, or in the case of bound systems simply mass, is a property of a particle or system of particles that remains constant regardless of the frame of reference in which it is measured.

  • For a single particle, the invariant mass is equal to the energy of the particle at rest divided by the square of the speed of light.
  • In the case of photons, which have zero rest mass, their invariant mass is calculated using their energy and momentum, which are related by the equation E = pc, where E is the energy, p is the momentum, and c is the speed of light.
  • In particle physics, invariant mass is an important concept because it is conserved in all interactions, including those that involve the conversion of mass into energy and vice versa.
  • The conservation of invariant mass is a consequence of the conservation of energy and momentum, which are fundamental principles in physics.