Lesson Objectives

  • Compare ways in which energy changes from one form to another.
  • Discuss what happens when a fuel burns.
  • Describe the difference between renewable and non-renewable resources.
  • Classify different energy resources as renewable or non-renewable.


Everything requires energy. Even while you are sitting as still as you possibly can, your body is using energy to breathe, circulate blood, digest food, and perform many other functions. Producing light or heat requires energy. Making something requires energy. Plants and animals all require energy to function.

The Need for Energy

Energy is the ability to do work or produce change. Every living thing needs energy to perform its daily functions and even more energy to grow. Plants get energy from the "food" they make by photosynthesis, and animals get energy directly or indirectly from that food.
People also use energy for many things, such as cooking food, keeping ice cream cold in the freezer, heating a house, constructing a skyscraper, or lighting your home. Because billions of people all around the world use energy, there is a huge need for energy resources (Figure below).
Electrical transmission tower.
Electrical transmission tower.

Electrical transmission towers like the one shown in this picture help deliver the electricity people use for energy every day.
The law of conservation of energy says that energy cannot be created or destroyed. This means that even though energy changes form, the total amount of energy always stays the same. How does energy get converted from one type to another when you kick a soccer ball? When your body breaks down the food you eat, it stores the energy from the food as chemical energy. But some of this stored energy has to be released to make your leg muscles move. So the chemical energy converts to another form of energy, called kinetic energy. Kinetic energy is the energy of anything in motion. Your muscles move your leg, your foot kicks the ball, and the ball gains kinetic energy from the kick. So you can think of the action of kicking the ball as a story of energy changing forms.
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To learn the quadratic equations related to getting a rapidly moving car to overcome its kinetic energy and come to a stop watch this video (I&E 1e): http://www.youtube.com/watch?v=v-Z2-jxCqVw&feature=related (6:01).
Potential energy is energy that is stored. Potential energy has the potential to do work or the potential to be converted into other forms of energy. If a ball is sitting on the very edge at the top of the hill, it is not moving, but it has a lot of potential energy.
Animations showing the conversion of potential energy to kinetic energy can be seen at the following sites.

Energy, Fuel, and Heat

If you read a book beneath a lit lamp, that lamp has energy from electricity. The energy to make the electricity comes from fuel. Fuel has energy that it releases. A fuel is any material that can release energy in a chemical change.
What are some examples of fuel and what are they used for?
  1. Food is fuel for your body.
  2. Sunlight is the energy plants need to make food by photosynthesis.
  3. Gasoline is fuel for cars.
  4. Hydrogen is fuel for the Sun.
For a fuel to be useful, its energy must be released in a way that can be controlled. Controlling the release of energy makes it possible for the energy to be used to do work. When fuel is used for its energy, it is usually burned, and most of the energy is released as heat. The heat may then be used to do work (Figure below). Think of a person striking a match to set some small twigs on fire. After the twigs burn for a while, they get hot enough to make some larger sticks burn. The fire keeps getting hotter, and soon it is hot enough to burn whole logs. Pretty soon the fire is roaring and a pot of water placed on the fire starts to boil. Some of the liquid water evaporates.

A controlled fire.
What is the source of energy for boiling and evaporating the water? Although some chemical energy from the match was put into starting the fire, the heat to boil and evaporate the water comes from the energy that was stored in the wood. The wood is the fuel for the fire.

Types of Energy Resources

Energy resources are either renewable or non-renewable. Non-renewable resources are used faster than they can be replaced so the supply available to society is limited (see example in Figure below). Renewable resources will not run out because they are replaced as quickly as they are used. Can you think of some renewable and non-renewable energy sources?
Anthracite coal.
Anthracite coal.

Anthracite coal is a non-renewable energy resource.

Non-renewable Resources

Fossil fuels - coal, oil, and natural gas are the most common example of non-renewable energy resources. Fossil fuels are formed from the partially decomposed remains of once living plants and animals - fossils. They took millions of years to form. When fossil fuels are burned for energy, they release pollutants into the atmosphere. Fossil fuels also release carbon dioxide and other greenhouse gases, which are causing global temperatures to rise. The environmental effects of fossil fuel use are discussed in the Climate and Human Actions and the Atmosphere chapters.

Renewable Resources

Renewable energy resources include solar, water, wind, biomass, and geothermal. These resources are either virtually limitless like the Sun, which will continue to shine for billions of years, or will be replaced faster than we can use them. Amounts of falling water or wind will change over the course of time, but they are quite abundant. Biomass energy, like wood for fire, can be replaced quickly. The use of renewable resources may also cause problems. Some are expensive or have uses other than for energy, such as trees. Some cause environmental problems. As the technology improves and more people use renewable energy, the prices may come down. And, as we use up fossil fuels, coal, oil, and natural gas will become more expensive. At some point, even if renewable energy costs are high, non-renewable energy will be even more expensive. Ultimately, we will have to use renewable sources. Energy conservation is something everyone can do that is needed even now.

Important Things to Consider about Energy Resources

With both renewable and non-renewable resources, there are at least two important things to consider. One is that we have to have a practical way to turn the resource into a useful form of energy. The other is that we have to consider what happens when we turn the resource into energy.
For example, if we get much less energy from burning a fuel than we put into making it, then that fuel is probably not a practical energy resource. On the other hand, if another fuel gives us large amounts of energy but also creates large amounts of pollution, that fuel also may not be the best choice for an energy resource.

Lesson Summary

  • According to the law of conservation of energy, energy is neither created nor destroyed.
  • Renewable resources can be replaced at the rate they are being used.
  • Non-renewable resources are available in limited amounts or are being used faster than they can be replaced.

Review Questions

  1. What is needed by anything that moves or changes in any way?
  2. What is the original source of most energy used on Earth?
  3. In what form does a living creature store energy from food?
  4. When we burn a fuel, what is released that allows work to be done?
  5. For biomass, solar, coal, natural gas, oil, and geothermal energy, identify each energy resource as renewable or non-renewable and explain why.
  6. What factors are important in judging how helpful an energy resource is to us?
  7. Is the energy from a rechargeable battery renewable? (A rechargeable battery can be recharged by being put into a device that is plugged into the wall.) Explain.

Further Reading / Supplemental Links


renewable resources Resources that are limitless or that are replaced more quickly than we can use them.. potential energy Energy stored within a physical system that has the potential to do work. non-renewable resources Resources that are being used faster than they can be replaced or their availability is limited to what is currently on Earth; e.g. fossil fuels. law of conservation of energy Law stating that energy cannot be created or destroyed. kinetic energy The energy that an object in motion has because of its motion. fuel Material that releases energy as it changes chemically. energy The ability to do work or change matter. chemical energy Energy that is stored in the chemical bonds in molecules.

Points to Consider

  • How long do fossil fuels take to form?
  • Are all fossil fuels non-renewable resources?
  • Do all fossil fuels affect the environment equally?
  • How is food energy measured?
  • Is a rechargeable battery a renewable source of energy?