Explanation:

the two extremities of the swing

-Pendulum, an object connected to a fixed support in such a way that it is free to swing back and forth under the influence of gravity. The typical pendulum consists of a weight, or bob, and a wire or slender rod by which the bob is suspended. At rest, the bob hangs directly below the point of support, if the bob is moved from this position and released, gravity causes it to swing back and forth along a circular arc at the end of the wire or rod. When the bob reaches the end of one swing, gravity causes it to begin to fall and gain speed as it moves downward. After it passes the lowest point in the swing, the bob begins to move upward along the arc. Gravity then causes the bob to slow down until it stops and begins to fall again: