Q. 15. Illustrate the law of conservation of energy by discussing the energy changes that 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?
In the above figure, point B is the mean position about which the bob rotates.
When the bob is released from point C, it attains some velocity while moving down (up to B), decelerates and stops at point A.
Thus point A and point C are the maximum height points. And the velocity of the bob at point B will be maximum.
The total energy at point A and point C is only the potential energy as its velocity at these points is zero. At point B, the height of the bob is zero; thus, the total energy is just the kinetic energy.
Thus, in this manner, the conservation of energy takes place (by transforming in some other form.).
The eventually comes to rest due to the air resistance. It decelerates the motion of the bob. (as it is a frictional force.)
There is no violation of the energy conservation law as some amount of energy is converted in the form of heat.