Hi, I'm trying to find out what the force of electromagnetic radiation would be, that pushes on a spherical black body. The radiation is a parallel beam of light. At first contact the photons would exchange all their momentum with the sphere. After that the energy would be radiated outward in a random direction. This would cancel out some of it's momentum that is exchanged with the radiation again. I only need the net momentum that is reflected from where the radiation came. Is there a formula to calculate this for spherical black bodies? What I've come up with so far is the function cos(∏x)*cos(∏x) and integrate it to find: ( ( (sin(2∏x))/2∏) + ∏x ) /2∏ For 0->x->1/2 the reflection would be 0,25 This is not spherical yet, I know. Please tell me what you think about it. Thanks!!