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Energy of a Pendulum

animation of the energy of an active pendulum
[QuickTime Version]

In this animation, you see a mass attached to the end of a string which forms a pendulum. The pendulum begins with only gravitational potential energy (GPE) since it is not moving yet. After being released, GPE is turned into kinetic energy (KE). Notice that no matter where the pendulum is, the sum of the GPE and KE is always equal to the original amount of energy the system started with. This demonstrates the Law of Conservation of Energy.


  1. Where does the pendulum have the highest velocity?
  2. How does the original height of the pendulum compare to its final height?

This simulation is assuming that there is no air friction and no friction in the pivot point of the rope.



1) The velocity of the pendulum is highest at the bottom of the arc.
2) The original height of the pendulum is the same final height of the pendulum (as long as no energy is considered lost to sound and friction).