Energy can never be created or destroyed — it can only be transformed from one form to another. For example, electric energy is converted to heat energy in an electric stove, to light energy in an electric bulb. On burning kerosene, chemical energy of the oil changes into heat energy. When you rub your palms together vigorously, they get heated. Mechanical energy is converted into heat energy.

When energy in one form disappears, it appears in another form and the total energy remains the same. This is the principle of conservation of energy. It is stated as follows:

• Energy can neither be created nor destroyed, but it can only be transformed from one form into another and can be transferred from one object to another.

Conservation of mechanical energy The sum of the potential and kinetic energies of an object is referred to as its mechanical energy, ME. Mechanical energy = potential energy + kinetic energy

ME = PE + KE

If friction effects are neglected, energy is transformed from potential energy to kinetic energy and vice versa, but the sum of the two is constant. Thus, mechanical energy is conserved when friction is absent.