It is all the energy that an object has because of its motion (kinetic energy) and its position (potential energy). Machines use mechanical energy to do work. For instance, a hammer uses mechanical energy to drive a nail into a board.

Most alternative energy sources are renewable, which means that, unlike fossil fuels, they are not likely to run out. Examples include the Sun, wind, rivers and oceans, heat from inside Earth, and biofuels.

By a somewhat complicated series of reactions, four hydrogen nuclei join together to form a new helium nucleus, giving off a great deal of energy in the process. This joining of nuclei is the source of all the energy emitted by the Sun.

Electric lightbulbs and neon lights change electrical energy, which may be produced by chemical, mechanical, or atomic energy, into light energy. Light sources are necessary for vision. An object can be seen only if light travels from the object to an eye that can sense it.

The term alternative energy refers to the use of renewable power sources in place of fossil fuels and other traditional sources of energy. Alternative energy is also called renewable energy. Sources of alternative energy include, among others, solar power, wind power, waterpower, and geothermal energy.

People and other animals can see because there is light. Light is a form of energy. The Sun is a very important source of light energy. Without the energy from the Sun, there would be no plants or animals on Earth’s surface.

Solar energy is light, heat, and other forms of energy given off by the Sun. Solar energy can be collected and used to heat buildings and to make electricity.

Geothermal energy is heat that comes from inside Earth. In some places, such as Iceland, the heat is so close to the surface it can be easily used as an energy source. In other places holes must be drilled down through rocks to reach the heat.

Fats are sources of energy that the body can store. The fats in foods may be solid or liquid. Liquid fats are called oils. The body uses fats to maintain its temperature and to cushion organs. Fats also help the body use certain vitamins. Cooking oils, nuts, fish, and avocados can be healthy sources of fat. But some fats can be harmful.

Wind power is an alternative energy source. This means that the power of the wind can be used in place of other energy sources such as coal , oil , and nuclear reactions . Wind can be used to produce electricity that heats homes and lights streets and buildings.