if photons are massless, how can it push something like a light sail, and how can sunlight adds weight to earth?

Question

if photons are massless, how can it push something like a light sail, and how can sunlight adds weight to earth?

In: 2

Answer 1

If c=1 (pretty much always the case because it makes math EZ) we have m^2 = E^2 − p^2 .

m = mass
E = energy
p = momentum

If m = 0 (as is the case of a photon) then it follows trivially that E = |p|. Or in other words a photon has momentum equal to its energy. The Planck Relation will give you the energy: 𝐸=ℎ𝜈 where ℎ is Planck’s constant, and 𝜈 is the frequency of the light.