What is conservation of energy

             Law of Conservation of Energy

Energy can be transformed (or change) from one form to another. According to the law of conservation of energy : Whenever energy changes from one form to another, the total amount of energy remains constant. In other words, when energy change from one form to another, there is no loss or gain of energy. The total energy before and after transformation remains the same. Another definition of the law of conservation of energy is that : Energy can neither be created nor destroyed.

              During the conservation of energy from one form to another, some energy may be wasted. For example, when electrical energy is converted into light energy in an electric bulb, then some electrical energy is wasted in the form of heat. 

Conservation of Energy During the Free Fall of a Body

The sum of potential energy and kinetic energy of the ball remains the same at every point during its free fall. The decrease in potential energy of the free falling ball at any point in its path appears as an equal increase in its kinetic energy. So, the total energy (potential energy + kinetic energy) of the ball remains the same at every point during it's free fall. Thus, the energy of a freely falling ball is conserved.

Conservation of Energy in a Simple Pendulum

    A swinging simple pendulum is an example of conservation of energy. This is because swinging simple pendulum is a body whose energy can either be potential or kinetic, or a mixture of potential and kinetic, but its total energy at any instant of time remains the same. Thus, a very simple illustration of the transformation of potential energy into kinetic energy, and of kinetic energy back into potential energy is given by a swinging simple pendulum (or an oscillation simple pendulum).

                 It should be noted that the body which does work loses energy and the body on which work is done, gains energy. For example, when we lift a stone from the ground and raise it to a height, we have to do some work on the stone. As a result of doing this work, we lose some energy from our body. On the other hand, the stone which we raised,  gains an equal amount of potential energy. Thus the total energy remains the same.