The law of conservation of energy is a principle of physics that states that, in a closed system, energy cannot be created or destroyed. It is expressed in the First Law of Thermodynamics, which states that energy may be transformed into many forms, such as light or heat, but the overall sum of the energies is conserved, or remains constant. Generally, this law is illustrated with a pendulum. The height at which the ball is released at one end of a pendulum will equal the height the ball will reach at the other end. In fact, in a theoretically frictionless environment, the ball will continue to swing back and forth forever.
As a fundamental concept in physics, the law of conservation of energy provides an explanation for how energy is conserved and converted within a system. Generally, one form of energy can be converted into another form of energy. For example, potential energy can be converted to kinetic energy.
The kinetic energy of a particular object is the energy it posses while in motion. As an expression, kinetic energy equals one-half of the mass of the object, multiplied by the square of the velocity of the object, or KE = 1/2mv2. Kinetic energy consists of three types of energies. Vibrational kinetic energy is the energy due to vibrational motion, and rotational kinetic energy is the energy due to rotational motion. Translational kinetic energy is the energy due to motion of the center of mass from one point to another.
Generally, the potential energy of an object is the energy that is stored while at rest in a force field. Gravity is a force that acts upon an object and gives it potential energy. For example, a ball at the top of a hill has a certain amount of stored energy due to gravity. Other types of potential energy include electric, magnetic, and elastic. An example of elastic potential energy is a stretched spring.
The law of conservation of energy states that the potential energy of a ball on a hill is generally converted to kinetic energy when the ball starts rolling down the hill as a result of gravity. Similarly, the potential energy of a stretched spring becomes kinetic energy when the spring is released. In a pendulum, the law establishes that, when the ball is at its highest point, all the energy is potential energy and there is zero kinetic energy. At the ball's lowest point, all the energy in the ball is kinetic and there is zero potential energy. The total energy of the ball is the sum of the potential energy and kinetic energy.