2007-10-13 20:10:59 · 5 answers · asked by lucylonglegs 1 in Science & Mathematics ➔ Physics
A photon has a rest mass of Zero.
In relativity, all the energy which moves along with the body adds up to the rest energy of the body, which is proportional to the rest mass of the body. Even a single photon traveling in empty space has a relativistic mass, which is its energy divided by c2.
Although a photon is never "at rest", it still has a rest mass, which is zero. If you chase a photon faster and faster, the observed energy of the photon approaches zero as the observer approaches the speed of light. This is why photons are massless. They have zero rest mass even though they have varying amounts of energy and relativistic mass. But, systems of two or more photons moving in different directions (as for example from an electron–positron annihilation) may have zero momentum over all. Their energy E then adds up to an invariant mass m = E/c2, when they are considered as a system.
2007-10-13 20:15:50 · answer #1 · answered by Anonymous · 4⤊ 0⤋
Its a meaningless question.
A photon cannot be at rest and has no rest frame (look up your special relativity). Hence the concept of rest mass for it is entirely meaningless.
2007-10-13 21:33:35 · answer #2 · answered by Anonymous · 1⤊ 0⤋
Photons can't stop.
Perhaps they don't even exist?
2007-10-13 20:23:06 · answer #3 · answered by bahbdorje 6 · 0⤊ 3⤋
zero
2007-10-14 03:25:50 · answer #4 · answered by mojorisin 3 · 0⤊ 0⤋
zero(0)
2007-10-13 20:18:37 · answer #5 · answered by brahma c 1 · 3⤊ 0⤋