1. The problem statement, all variables and given/known data The two blocks (m=16kg and M=88kg) are not attached to each other. The coefficient of static friction between the blocks is us=0.38, but the surface beneath the larger block is frictionless. What is the minimum magnitude of the horizontal force F required to keep the smaller block from slipping down the larger block? (I've attached the figure in this thread) 2. Relevant equations Let F be the force applied and F' be the Force of the system F = mg/[us(1-[m/(m+M)])] 3. The attempt at a solution I already know the solution to the problem but I'm having a hard time seeing why the normal force of the smaller block is equal to the total force of the whole system, not to the force applied to the smaller block.