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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
A pendulum is a body which hangs from a fixed point and shows back and forth motion.
When bob is on right side, not released
When the bob of Pendulum is pulled to right side and not yet released
Since it has some height and it is not moving
It has Potential Energy but not Kinetic Energy
(Suppose Potential Energy = 10 J, Kinetic Energy = 0 J, Total Energy = 10 J)
When bob is released
When bob is released from hand, the bob loses potential energy and gains kinetic energy
(Suppose Potential Energy decreases to 8 joules, Kinetic Energy becomes 2 joules, Total = 10 Joules)
When it reaches center position
It has only kinetic energy but no potential energy
(Suppose Potential Energy = 0J, Kinetic Energy = 10J, Total Energy = 10J)
When bob goes left
This kinetic Energy makes the bob move towards left side
As it moves upwards towards other side, kinetic energy decreases and potential energy increases
(Suppose Potential Energy = 2, Kinetic Energy = 8J, Total Energy = 10J)
When bob reaches max left side
It soon reaches a point where potential energy becomes maximum and kinetic energy becomes 0
(Suppose Potential Energy = 10J, Kinetic Energy = 0 J, Total Energy = 10J)
Hence, Total Energy in all cases remain constant at 10 Joules
Hence, the law of conservation of energy is not violated in case of a simple pendulum since the energy is always conserved.
Eventually the bob comes to rest
During each oscillation, some energy gets transferred to the air due to overcome air friction.
So, Kinetic Energy of pendulum is lost due to air friction and the pendulum stops
