What does it mean when we say that a physical magnitude, in this case Mechanical Energy, is conserved?
Throughout these pages we have emphasized that there are many types of energy.  We have concentrated on potential gravitational energy and kinetic energy.  Both are characteristics of a freely falling body.  We have seen that the sum of its values remains constant.  What exactly does this mean?  It means that a physical magnitude like energy has the property of being able to transform itself from one form into another, so that the decrease in one means an increase in another or others.

Man has managed to take advantage of this property of energy.  We have developed ways to transform some forms of energy into other more exploitable forms: potential gravitational energy into electric energy, electric energy into lighting, chemical energy into heating...
In the case of the free fall phenomenon only kinetic and potential energy are involved and so the decrease/increase in one means an increase/decrease in the other. 

The transformation from one form of energy to another is a phenomenon which in certain cases is easily produced.

The following simulation presents a very everyday fact: an object bounces on a seesaw and transmits its energy to the other side.  This is one more example of the conservation of mechanical energy.

LEARN:

The energy a body possesses in one form can be transformed into other forms and in total will always have the same value...Does this mean it can always be used by man?