1. The problem statement, all variables and given/known data In the figure a block of mass 'm' is placed on a wedge of mass M. The wedge is subject to a horizontal force 'F' and slides on a friction less surface. The coefficient of static friction between the block and wedge is μs. Find the range of values of 'F' for which the block does not slide on the incline. 2. Relevant equations If the bodies (block+wedge) move together then: F=(M+m)a 3. The attempt at a solution If 'F' is too less, then the block of mass 'm' will have a tendency to come down the incline. If 'F' is too much, the block will have a tendency to move up the incline. So 'F' need to be in between these minimum and maximum values and that's how we get the range. But my doubt is that why do the above 2 conditions i.e when F is too less and when F is too much happen?