Q. 15. 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?
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 (upto B) and deaccelerated and stops at point A.
Thus point A and point C are the maximum height points. And the velocity of 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. And at point B as the height of 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 deacceleration the motion of 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.