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?

AcademicPhysicsNCERTClass 9

Law of conservation of energy: "Energy can neither be created nor can be destroyed, it can be converted from one form to another form." 

For example- 1. In a simple pendulum, at every position kinetic energy and potential energy get converted from one form to another form. While the total energy of the bob remains constant.

2. Potential energy of a freely falling body gets converted into kinetic energy.

Law of conservation of energy with the help of a pendulum:

A simple pendulum is an example of the conservation of energy. It can be understood as:

1. At center position B only Potential energy it has.

2. While moving down towards center A Potential energy starts decreasing and kinetic energy starts increasing.

3. At center A Potential energy is zero and the bob of the pendulum has only kinetic energy.

4. While the bob moves from center A to Extreme position B kinetic energy starts decreasing and potential energy starts increasing. 

5. At extreme position C the pendulum has only potential energy.

The bob eventually comes to rest as it losses its kinetic energy to overcome the air friction or air resistance offered by the surroundings and stops after some time.

When the pendulum stops eventually, it does not violate the law of conservation of energy as it losses its kinetic energy to overcome the air resistance, then this kinetic energy is gained by the surrounding system and energy remains conserved.

Updated on 10-Oct-2022 13:22:57