Posted by **Tiffany** on Tuesday, June 2, 2009 at 3:12pm.

do gamma rays carry momentum? i thought they don't because they don't have mass so mv=0 but my frend says even tho they don't have mass they still carry momentum. how does this make sense? please help.

- momentum -
**Damon**, Tuesday, June 2, 2009 at 3:32pm
Photons in general carry momentum so any electromagnetic wave has momentum associated with it despite its lick of rest mass in the classical sense. If a photon hits something, it moves it.

E = energy of photon = m c^2 = h f where c is velocity of light and h is plank constant and f is the frequency

Of course we know classical rest mass m is zero but that does not prove there is no energy, m c^2 at the velocity of light.

then m c = momentum p

but m c = E/c

so p = E/c

but E = h f

so

momentum p = h f /c

but f/c = 1/Tc = 1/Lambda

where T is period and Lambda is wavelength

so

p = h/Lambda

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