Conservation of Energy

Energy can be neither created nor be destroyed, but it may change forms and be transferred from and to different objects in a never-ending cycle.

In physics, the law of conservation of energy states that the total energy (supply?) of an isolated system will not, should not, and cannot change—it is said to be conserved over time.

The law states that the total amount of energy present, has been there since the very start and will continue to stay at that amount. During the (incredibly long) time span that energy existed, it would have changed forms millions upon millions of times every time something happens. 

Say, when a coconut fell from a tree and unto the ground- potential energy changes into kinetic energy. Once it hit the ground, bounces a few times and stops moving- it turns into potential again.

But during those events, the energy never disappeared. It just keeps changing, and changing, and changing. Whether it may be from potential to chemical to kinetic to thermal. It just kept changing, and will continue to do so until the end of time.

And that, is the law of energy conservation in a nutshell. It should be noted that the conservation of energy only applies to hypothetical isolated systems and may (or may not) apply to exposed systems.