Active Reading Solution: Motion in a Potential Well

Because systems tend to accelerate toward regions of low potential energy, the object begins by moving to the right. It picks up speed as it moves: that is, it converts potential energy to kinetic energy.
At x=b the object reaches its minimum potential energy and its maximum speed.
To the right of x=b the object is still moving to the right (because of the built-up inertia) but the force is now pushing it to the left, causing it to slow down.
The object comes momentarily to rest at x=c, at a spot where U(x) is exactly as high as it was at x=a. That is to say, the kinetic energy has now been converted back to potential energy.
Then the object begins to move leftward again. It will rock back and forth between x=a and x=c forever.