Did you know that everything you do takes energy? Even while you are sitting still, your body is using energy to breathe, to keep your blood circulating, and to control many different processes. But it's not just you. Everything that moves or changes in any way—from plants to animals to machines—needs energy. Have you ever wondered where all of this energy comes from?
- Compare ways in which energy is changed from one form to another.
- Discuss what happens when we burn a fuel.
- Describe the difference between renewable and nonrenewable resources, and classify different energy resources as renewable or nonrenewable.
The Need for EnergyEdit
Energy can be defined as the ability to move or change matter. Every living thing needs energy to live and grow. Your body gets its energy from food, but that is only a small part of the energy you use every day. Cooking your food takes energy, and so does keeping it cold in the refrigerator or the freezer. The same is true for heating or cooling your home. Whether you are turning on a light in the kitchen or riding in a car to school, you are using energy all day long. And because billions of people all around the world use energy, there is a huge need for resources to provide all of this energy. Why do we need so much energy?
The main reason is that almost everything that happens on Earth involves energy. Most of the time when something happens, energy is changing forms.
Even though energy does change form, the total amount of energy always stays the same. The Law of Conservation of Energy says that energy cannot be created or destroyed. Scientists discovered this law by noticing that any time they observed energy changing from one form to another, they could measure that the overall amount of energy did not change.
For an example of how energy changes from one form to another, think about what goes on when you kick a soccer ball. Your body gets its energy from food. When your body breaks down the food you eat, it stores the energy from the food in a form called chemical energy. But some of this stored energy has to be released to make your leg muscles move. When this happens, the energy that is released changes from chemical energy to another form, 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 by being kicked. So you can think of the action of kicking the ball as a story of energy moving and changing forms. The same is true for anything that happens involving movement or change. 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. An example of potential energy might be the ball you kicked, if it ended up at the top of a hill.
Energy, Fuel, and HeatEdit
As you have learned, energy is the ability to move or change matter. To put it another way, you could say that energy is the ability to do work. But what makes energy available whenever you need it? If you have ever accidentally unplugged a lamp while you were using it, you have seen that the lamp does not have a supply of energy to keep itself lit. When the lamp is plugged into an outlet, it has the source of energy it needs—electricity. The electricity comes from a power plant, and the power plant has to have energy to produce this electricity (Figure 5.1). The energy to make the electricity comes from a fuel, which stores the energy and releases it when it is needed. A fuel is any material that can release energy in a chemical change. The food you eat acts as a fuel for your body. You probably hear the word fuel most often when someone refers to its use in transportation. Gasoline and diesel fuel are two fuels that provide the energy for most cars, trucks, and buses. But many different kinds of fuel are used to meet the wide variety of needs for energy storage.
For a fuel to be useful, its energy must be released in a way that can be controlled. Controlling the release of the energy makes it possible for the energy to be used to do work. When a fuel is used for its energy, the fuel is usually burned, and most of the energy is released as heat. The heat can be used to do work. For an example of how the energy in a fuel is released mostly as heat, think about what happens when someone starts a fire in a fireplace. First, the person strikes a match and uses it to set some small twigs on fire. After the twigs have burned 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.
You might think at first that the heat comes from starting the fire. After all, someone struck a match to start the fire, and then the fire just spread, right? But if you think about this fire in terms of energy, almost all of the heat comes from the energy that has been stored in the wood. In other words, the wood is the fuel for the fire. There is a reason why it is easy to be confused about the source of the fire’s heat. The reason is that some energy has to be put into starting the fire before any energy can come out of the fire. At first, there is energy stored in the head of the match as chemical energy. When someone strikes a match, this chemical energy is released as heat.
The lit match gives off enough heat to set the twigs on fire. This heat is enough energy to start changing the chemical energy in the wood (and the oxygen in the air, which the wood needs in order to burn) into heat. What happens is that the heat from the match breaks chemical bonds in the twigs. When these bonds break, the atoms in the twigs are free to move around and form new bonds. When the atoms form new bonds, they release more heat. This heat causes more and more of the wood to change its stored chemical energy into heat. So, what started as a fairly small amount of heat from the match turns into a much, much larger amount of heat from the wood. The same thing is true for any fuel. We have to add some energy to the fuel to get it started. But once the fuel starts burning, it keeps changing its chemical energy into heat. As long as the conditions are right, the fuel will keep turning its energy into heat until the fuel is all gone.
Types of Energy ResourcesEdit
Energy resources can be put into two categories—either renewable or nonrenewable. Resources that are nonrenewable are used faster than they can be replaced (Figure 5.2). Other resources that are called renewable will never run out. In most cases, these resources are replaced as quickly as they are used.
In a way, the difference between nonrenewable and renewable resources is like the difference between ordinary batteries and rechargeable ones. If you have a flashlight at home that uses ordinary batteries, and you accidentally leave the flashlight on all night long, you will need to buy new batteries once the ones in the flashlight have died. The energy in the ordinary batteries is nonrenewable. But if the flashlight has rechargeable batteries, you can put them in a battery charger and use them in the flashlight again. In this way, the energy in the rechargeable batteries is "renewable".
Fossil fuels are the most common example of nonrenewable energy resources. Renewable energy resources include solar, water, and wind power. If you traced the energy in all of these resources back to its origin, you would find that almost all energy resources—not just solar energy—come from the sun. Fossil fuels are made of the remains of plants and animals that stored the sun's energy millions of years ago. These plants and animals got all of their energy from the sun, either directly or indirectly. The sun heats some areas more than others, which causes wind. The sun's energy drives the water cycle, which moves water over the surface of the Earth. Both wind and water power can be used as renewable resources.
Types of Nonrenewable ResourcesEdit
Fossil fuels, which include coal, oil, and natural gas, are nonrenewable resources. Millions of years ago, plants used energy from the sun to form sugars, carbohydrates, and other energy-rich carbon compounds that were later transformed into coal, oil, or natural gas. The solar energy stored in these fuels is a rich source of energy, but while fossil fuels took millions of years to form, we are using them up in a matter of decades and will soon run out. Fossil fuels are nonrenewable resources. The burning of fossil fuels also releases large amounts of the greenhouse gas carbon dioxide.
Types of Renewable ResourcesEdit
Renewable energy resources include solar, water, wind, biomass, and geothermal power. These resources can usually be replaced at the same rate that we use them. Scientists know that the sun will continue to shine for billions of years and we can use the energy from the sun as long as we have a sun. Water flows from high places to lower ones and wind blows from areas of high pressure to areas of low pressure. We can use the flow of wind and water to generate power and we can count on wind and water to continue to flow. Some examples of biomass energy are burning something like wood or changing grains into biofuels. We can plant new trees or crops to replace the ones we use. Geothermal energy uses water in the rocks that has been heated by magma. The magma will heat more water in the rocks as we take hot water out.
Even renewable resources can come with problems, though. We could cut down too many trees or we might need grains to be used for food rather than biofuels. Some renewable resources have been too expensive to be widely used or cause some types of environmental problems. As the technology improves and more people use renewable energy, the prices may come down. And, as we use up fossil fuels, they will become more expensive. At some point, even if renewable energy is expensive, nonrenewable energy will be even more expensive. Ultimately, we will have to use renewable sources (and conserve).
Important Things to Consider About Energy ResourcesEdit
With both renewable and nonrenewable 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.
- According to the law of conservation of energy, energy is neither created or destroyed.
- Renewable resources can be replaced at the rate they are being used.
- Nonrenewable resources are available in limited amounts or are being used faster than they can be replaced.
- What is needed by anything that moves or changes in any way?
- What is the original source of most of our energy?
- When your body breaks down the food you eat, in what form does it store the energy from the food?
- When we burn a fuel, what is released that allows work to be done?
- For biomass, coal, natural gas, oil and geothermal energy, identify each energy resource as renewable or nonrenewable. Explain your reasoning.
- What factors are important in judging how helpful an energy resource is to us?
- Is a rechargeable battery a renewable source of energy? Explain.
- chemical energy
- Energy that is stored in the connections between atoms in a chemical substance.
- The ability to move or change matter.
- Material that can release energy in a chemical change.
- kinetic energy
- The energy that an object in motion has because of its motion.
- law of conservation of energy
- Law stating that energy cannot be created or destroyed.
- potential energy
- Energy stored within a physical system.
Points to ConsiderEdit
- How long do fossil fuels take to form?
- Are all fossil fuels nonrenewable resources?
- Do all fossil fuels affect the environment equally?