Let's see what happens when I release it:
Let's begin (as do the graph and the animation) with the mass to the right of equilibrium and at rest. (The graph is rotated 90° from its normal orientation so that we can compare it with the motion.) To the right of equilibrium, the force acts to accelerate the mass to the left, and vice versa. Because there are no vertical displacements, we discuss here only the horizontal displacement.Īt the equilibrium position (x = 0 in the graph below the clip), the forces exerted by the two springs are equal in magnitude but opposite in direction, so the total force is zero. Consequently, the only non-negigible force in the horizontal direction is that exerted by the two springs. Because the speed is small, air resistance is very small.
So the mass is supported, like a hovercraft, on a cushion of air, and friction is eliminated. The track is perforated with small holes, through which flows air from the inside, where the pressure is above atmospheric. In the slow motion movie clip at right, the mass glides on an air track.
