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 a violation of the law of conservation of energy?

Answer 1

Law of Conservation of Energy: Pendulum Example

Step 1: Drawing the pendulum bob to one side
When we pull a pendulum bob to one side, we do work on it, giving it gravitational potential energy (PE). At this point, its kinetic energy (KE) is zero.

Step 2: Releasing the bob
As the bob swings downward, its potential energy is converted into kinetic energy. At the lowest point of the swing, the bob has maximum kinetic energy and minimum potential energy.

Step 3: Swinging to the other side
As the bob moves upward, its kinetic energy is converted back into potential energy. This energy conversion continues with every swing, illustrating the law of conservation of energy: energy is not lost, only transformed from one form to another.

Why does the bob eventually come to rest?
In reality, due to air resistance and friction at the pivot, some energy is gradually transformed into heat energy and sound. This reduces the mechanical energy of the pendulum, so the bob slows down and eventually stops.

What happens to its energy eventually?
The mechanical energy of the pendulum is converted into heat and sound energy in the surroundings. Energy is not destroyed; it is just transformed.

Is it a violation of the law of conservation of energy?
No. The law of conservation of energy is not violated because the total energy, including the energy transformed into heat and sound, remains constant in the universe.