Energy is the ability to do work. It can come in the forms of heat and light. There are two types of energy: working energy and stored energy. Stored energy becomes working energy when we use it.
You eat food for energy. Then your body stores the energy until you need it. When you work and play, your stored energy becomes working energy.
We use energy every day. We use it to grow our food, warm and cool our homes, make our electricity, run our cars, and make products like clothes and toys. It is a very important part of our lives. Most of the time, we use stored energy for fuel. Burning fuel sets the stored energy free in the form of heat. Long ago, people only burned wood as fuel. Now, we mostly burn “fossil fuels”—oil, natural gas, and coal.
They are called fossil fuels because they are formed over millions of years from the fossils, or remains, of dead animals and plants. The fossils became buried under dirt and rock. Heat from the earth and pressure from dirt and rock changes these fossils into oil, natural gas, and coal. Because it takes millions of years to make, or “renew,” more fossil fuels, we call them “nonrenewable fuels.”
Other fuels are called “renewable fuels” because they are “renewed” all the time and will never run out. One example of a renewable fuel is solar energy. Energy from the sun can be turned into electricity or heat.
Another kind of fuel is nuclear energy. Nuclear energy uses special radioactive materials to make electricity. Many people believe that nuclear energy is a clean, renewable energy. But making electricity this way leaves behind radioactive wastes that must be stored safely for thousands of years.