1. The problem statement, all variables and given/known data What is the magnitude of force F (which is pushing from the left on M) required to keep M1 and M2 relatively at rest to M? Ignore all friction. See attached diagram 2. Relevant equations Newton's laws 3. The attempt at a solution Well...If M is at rest, M1 and M2 will have an acceleration due to M2's weight. When force F appears though, M2 will be pushed horizontally by M since they are in contact. That's all I know atm.