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Energy is the ability or capacity to do work or to produce change. We often speak of needing energy to do work as human beings. There are different forms of energy such as heat, light, sound, electricity, and chemical energy.
There are two categories of energy. One is kinetic energy which is the energy an object has while it is in motion. The other is potential energy which is the energy a body has that is at rest but could exhibit due to its place and condition. Even when an object is at rest. The atoms and molecules within The object move about so in a sense even objects at rest have kinetic energy. The molecules within The object move faster as The temperature increases.
An example of potential and kinetic energy could be an apple on a table. It has The potential energy to fall by The force of gravity. If a sufficient push occurs, The apple can tumble over The table to The ground. The work that occurred to make this happen can be measured mathematically by this formula:
Work = Force (The amount of energy needed or used) times The distance to do The task.
It is common for energy to be converted from one form to another. The law of conservation of energy states that although energy can be changed in form it can be neither created nor destroyed. The theory of relativity by Albert Einstein shows that mass and energy are equal and thus that one can be converted into The other. Therefore The law of conservation of energy includes both mass and energy.