Energy is the ability to do work
Energy comes in different forms:
- Heat (thermal)
- Light (radiant)
- Motion (kinetic)
- Nuclear energy
People use energy for everything from making a jump shot to sending astronauts into space.
There are two types of energy:
- Stored (potential) energy
- Working (kinetic) energy
For example, the food a person eats contains chemical energy, and a person's body stores this energy until he or she uses it as kinetic energy during work or play.
Energy sources can be categorized as renewable or nonrenewable
When people use electricity in their homes, the electrical power was probably generated by burning coal, by a nuclear reaction, or by a hydroelectric plant on a river, to name just a few sources. Therefore, coal, nuclear, and hydro are called energy sources. When people fill up a gas tank, the source might be petroleum refined from crude oil or ethanol made by growing and processing corn.
Energy sources are divided into two groups:
- Renewable (an energy source that can be easily replenished)
- Nonrenewable (an energy source that cannot be easily replenished)
Renewable and nonrenewable energy sources can be used as primary energy sources to produce useful energy such as heat or used to produce secondary energy sources such as electricity.
When people use electricity in their homes, the electrical power was probably generated from burning coal or natural gas, a nuclear reaction, or a hydroelectric plant on a river, to name a few possible energy sources. The gasoline people use to fuel their cars is made from crude oil (nonrenewable energy) and may contain a biofuel (renewable energy) like ethanol, which is made from processed corn.
The chart below shows the energy sources used in the United States. Nonrenewable energy sources accounted for about 90% of all energy used. Biomass, which includes wood, biofuels, and biomass waste, is the largest renewable energy source, and it accounted for about half of all renewable energy and about 5% of total U.S. energy consumption.
There are five main renewable energy sources:
- Solar energy from the sun
- Geothermal energy from heat inside the earth
- Wind energy
- Biomass from plants
- Hydropower from flowing water
Most of the energy consumed in the United States is from nonrenewable energy sources:
Crude oil, natural gas, and coal are called fossil fuels because they were formed over millions of years by the action of heat from the earth's core and pressure from rock and soil on the remains (or fossils) of dead plants and creatures like microscopic diatoms. Most of the petroleum products consumed in the United States are made from crude oil, but petroleum liquids can also be made from natural gas and coal.
Nuclear energy is produced from uranium, a nonrenewable energy source whose atoms are split (through a process called nuclear fission) to create heat and, eventually, electricity.