Where does this young basketball player get his energy?
He gets his energy from the Sun. Not directly, of course. He eats food, which used sunlight to grow, or he eats something that ate something that used sunlight to grow. When he shoots the ball, some of the energy goes into the ball and hopefully the ball goes into the hoop. Two points!
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 their homes. Because billions of people all around the world use energy, there is a huge need for energy resources. Energy conservation is something everyone can do now to help reduce the strain on energy resources.
Conservation of Energy
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. The chemical energy is converted 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.
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.
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?
- Food is fuel for your body.
- Sunlight is the energy plants need to make food by photosynthesis.
- Gasoline is fuel for cars.
- 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 (Figure below). The heat may then be used to do work. 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.
- Energy is the ability to do work. Energy cannot be created or destroyed; it can only change form.
- Fuel stores energy that can be released during use.
- Heat is the motion of atoms due to the use of energy.
- Give an example of how the law of conservation of energy works.
- Compare and contrast chemical energy, kinetic energy, and potential energy.
- Think about a candle flame and a bathtub full of hot water. Which has the highest temperature and which has the highest heat? What's the difference?
Use this resource to answer the questions that follow.
- How can the energy of a weight at the top of a pulley be transferred into heat in a tub of water? List the types of energy involved.
- What is true about energy in a closed system?
- What are the two things that energy can become in a closed system?
- Where is the energy to drive a car stored and what type is it? What type of energy does that become?