Law of Conservation Of Energy

Energy in a system may take on various forms (e.g. kinetic, potential, heat, light). The law of conservation of energy states that energy may neither be created nor destroyed. Therefore the sum of all the energies in the system is a constant.

The most commonly used example is the pendulum:

The formula to calculate the potential energy is:
                                                                      

PE + KE = 0 PE = -KE
The sum of PE and KE is the total mechanical energy:

Total Mechanical Energy = PE + KE NOTE: This is with the abscence of outside forces such as friction

Using our common sense we know that it's impossible for the pendulum to swing higher than the height h without giving it a push yourself. If there was no friction, the pendulum would swing back and forth forever because of the law of conservation of energy.

  Prof. Walter Lewin demonstrates the conservation of mechanical energy.