1. The problem statement, all variables and given/known data Consider two blocks of mass M1 and M2. Mass M1 is resting on top of M2, which rests on a horizontal surface. The coefficient of static friction between the two blocks is u1 and the coefficient of kinetic friction between the bottom block and the ground is u2. A force F is applied to the bottom block at an angle R to the horizontal. The blocks move together in the horizontal direction. Draw a FBD for each block separately. 2. Relevant equations None yet. 3. The attempt at a solution This is what I have so far, but I don't understand the frictional forces acting between the blocks very well. I know static friction is keeping m1 on top of m2, but then it would be going to the right to oppose the motion of m1, but what would I balance that force with then? Any help is much appreciated.