The law of conservation of energy and mechanical systems

Conservation of Energy

The most fundamental principle of the "The Law of the Conservation of Energy" is that energy cannot be created or destroyed. The total sum of the energy of any system is always constant. However, energy can take on different forms -- potential, kinetic, heat, light, energy -- and can be converted from one form to another. For example, when a pendulum swings it possesses both potential and kinetic energy, or when a train is going up and down a hill. At the top of a hill a train has a large amount of potential energy, but it has very little kinetic energy. For a train at the bottom of a hill the opposite is true. When the pendulum swings from to one side, it is reducing its kinetic energy and increasing its potential energy, or vice versa, depending on the degree of the arc. When the train is at the top and bottom of the hill there is hardly any potential or kinetic energy being used at all and as the pendulum stops briefly on its arc both its kinetic energy and potential energy are likewise hardly being used but as the pendulum swings to the other side its level of kinetic energy again increases and its potential energy decreases until it swings back. ("Kinetic and Potential Energy," 2008, Thinkquest).

The pendulum or train's mechanical energy is the sum of its kinetic and potential energy ("Kinetic and Potential Energy," 2008, Thinkquest). Because energy cannot be created or destroyed, the pendulum would continue to swing forever, unless it interacted with another energy system, like the hand of a person who caused it to stop swinging entirely, through the use of static friction. A person's hand could also add its own energy to the energy of the pendulum's system by pushing the pendulum and causing it to swing farther than its original arc ("The Law of the Conservation of Energy," 2008, Thinkquest).