Energy is defined as the ability to do work, which can be thought of as the ability to cause some kind of change. Energy can take many different forms, and the most common forms of energy are potential energy and kinetic energy.

Potential energy is stored energy and the energy of position. Examples of potential energy include:

• Chemical energy: energy stored in the bonds of atoms and molecules. Batteries, biomass, petroleum, natural gas, and coal are examples of chemical energy. Chemical energy is converted to thermal energy when people burn wood in a fireplace or burn gasoline in a cars engine.
• Gravitational energy: energy stored in an objects height. The higher and heavier the object, the more gravitational energy is stored. When a person rides a bicycle down a steep hill and picks up speed, the gravitational energy is converted to motion energy. Hydropower is another example of gravitational energy, where gravity forces water down through a hydroelectric turbine to produce electricity.
• Mechanical energy: energy stored in objects by tension. Compressed springs and stretched rubber bands are examples of stored mechanical energy.

Kinetic energy is the energy of motion. Examples of kinetic energy include:

• Motion energy: energy stored in moving objects. The faster an object moves, the more energy is stored. Examples of motion energy include wind, a flowing river, a moving car, or a person running.
• Radiant energy: electromagnetic energy that travels in transverse waves. Radiant energy includes visible light, x-rays, gamma rays, and radio waves. Light is one type of radiant energy. Sunshine is radiant energy, which provides the fuel and warmth that make life on earth possible.
• Thermal energy: the energy associated with the constant, random bouncing of atoms or molecules. This is also called kinetic energy. The greater the thermal energy, the greater the kinetic energy of atomic motion, and vice versa.

Other forms of energy include:

• Electrical energy: energy associated with the movement of electrons.
• Sound energy: the movement of energy through substances. It moves in waves and is produced when a force makes an object or substance vibrate.
• Elastic energy: energy stored in objects when they are compressed or stretched.
• Nuclear energy: energy stored in the nucleus of an atom.

Energy is never lost, but it can be converted from one form to another[[6]](...