The law of conservation of energy states that in an isolated system the total energy remains constant—it is said to be conserved over time. Energy can neither be created nor be destroyed, but it can change from one form to another form. for instance,
1. Mechanical energy, such as the kinetic energy of motion, can be converted to heat energy
eg. in the heating of a car’s brakes when it slows down. Chemical energy in the gasoline of the car can be converted into both heat energy in the exhaust and heating the engine, and into mechanical energy to move the car.
2.Potential energy such as the gravitational potential energy stored in an object which is on a high shelf, can be converted into kinetic energy as the object falls down.
3.Electrical energy can be converted to heat or mechanical energy or sound energy in a variety of useful ways around the house using common appliances.
From these examples it is evident that energy can neither be created nor destroyed it can only be changed from one form to another desired form.