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 they use it 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 recreated)
Renewable and nonrenewable energy sources can be used to produce secondary energy sources like electricity.
There are five main renewable energy sources:
- Solar energy from the sun, which can be turned into electricity and heat
- Wind energy
- Geothermal energy from heat inside the earth
- Biomass from plants, which includes firewood from trees, ethanol from corn, and biodiesel from vegetable oil
- Hydropower from hydroelectric turbines
People get most of their energy from nonrenewable energy sources, which include fossil fuels (oil, natural gas, and coal). These energy sources 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. Another nonrenewable energy source is uranium, whose atoms can be split (through a process called nuclear fission) to create heat and eventually electricity.
People use renewable and nonrenewable energy sources to generate the electricity needed for homes, businesses, schools, and factories. Electricity powers computers, lights, refrigerators, washing machines, and heating and cooling systems.
Most of the gasoline used in cars and motorcycles, and the diesel fuel used in trucks, tractors, and buses are both made from crude oil and other hydrocarbon liquids that are nonrenewable resources. Natural gas, used to heat homes, dry clothes, and cook food, is also a nonrenewable resource.
The chart above shows what energy sources the United States used in 2014. Nonrenewable energy sources accounted for 90% of all energy used in the nation. Biomass, which includes wood, biofuels, and biomass waste, is the largest renewable energy source accounting for about half of all renewable energy and 5% of total energy consumption.