A block is resting on an inclined surface. Initially, the angle of the incline is small enough that the block is held in place by static friction. You can increase the angle of the incline using the slider. Eventually the block will begin to slide down the incline. Use the smallest angle at which the block slides to determine the coefficient of static friction between the block and the incline.
You can adjust the mass of the block in the simulation. Will that change the angle at which the block begins to slide? What does depend on the mass, if anything?