Illustrate the law of conservation of energy by discussing the energy changes which occur when we draw a pendulum bob to one side and allow it to oscillate. Why does the bob eventually come to rest? What happens to its energy eventually? Is it a violation of the law of conservation of energy?
A small metallic ball (called bob) suspended by a light string (thread) from a frictionless, rigid support is called a simple pendulum. A simple pendulum is shown in figure.
The bob of a simple pendulum swings from one extreme position to the other through its mean position.
The bob is at its highest position at the extreme positions and at lowest at its mean position. The energy changes which occur during the motion of the bob are shown in figure. So, when a pendulum swings to and fro, its energy changes constantly in the following sequence.
Extreme right position -All P.E. No K.E.
↓
Mean position - No P.E. All K.E
↓
Extreme left position -All P.E. No K.E
↓
Mean position -No P.E All K.E.
↓
Extreme right position -All P.E. No K.E