Question

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 violation of the law of conservation of energy.

Answer 1

The illustration is below in attachment...It comes to rest because air resistance resists its motion. The pendulum loses its kinetic energy to overcome this friction and stops after some time.

The law of conservation of energy is not violated because the energy lost by the pendulum to overcome friction is gained by its surroundings. Hence, the total energy of the pendulum and the surrounding system remain conserved.

Answer 2

Law of Conservation of Energy: Energy cannot be created and cannot be destroyed. We can only change one form of energy into another form.

Let us take the case of a simple pendulum. Its mean position is O and extreme positions are A and B.

simple pendulum

When the pendulum moves to point A, it reaches the maximum height. At this stage, the potential energy of the bob is maximum and kinetic energy is zero.

When the pendulum moves to point O, it reaches its mean position. At this stage, the kinetic energy of the bob is maximum and potential energy is zero.

In both the cases, the sum of kinetic energy and potential energy remains constant. Thus, the pendulum obeys the law of conservation of energy.

But the pendulum does not keep on oscillating forever. It eventually comes to rest. This happens because of air resistance. Some of the energy of the bob is utilized in overcoming the air resistance. This energy is taken up by the surrounding. In this case also, the total energy of the system remains constant. Hence, it does not violate the law of conservation of energy.fgf