What is energy? Most of us have a feeling that we understand energy and recognize it when we see it, but coming up with a formal definition might be harder for us to do. Here are some of the basic concepts associated with a definition of energy:

• Energy is required to make things change.
• Energy is the ability to do work. The kind of work we are talking about is not like going to a job or doing chores. We are talking about work as defined in the physical sciences.
• Work is the application of a force to move an object in the direction of the force, such as when you pedal a bicycle or an electric motor lifts an elevator.
• A force is an influence that can cause an object to move or stop an object that is already moving. Think about how brakes must be applied to slow an automobile, or how you throw a ball hard to get it to go as far as possible.
• Motion is a change in distance over time.
  

One of the easiest ways to recognize energy is to know the various forms it can take. All energy falls into two categories, kinetic and potential energy. Kinetic energy is the energy of motion. Think about the energy in a brick. Which has more energy, a brick lying on your foot, or a brick dropped on your foot? The dropped brick has more kinetic energy.

Energy is not an object in itself; rather, energy refers to a condition or state of an object.

The main types of kinetic energy are:

• Electrical Energy—The energy associated with the movement of electrons. When electrons flow through wires, we call it electricity.
• Thermal Energy—The energy that results from the movement of atoms and molecules and is related to their temperature. The faster the particles move, the greater the amount of energy and the higher the temperature.
• Movement Energy—When objects or materials flow or move from one place to another they produce energy, such as water flowing through a dam.
• Sound Energy—Produced by the periodic movement of matter in a medium. Sound can travel through air, solids and liquids, but not through a vacuum, because there is no matter there.
• Radiant Energy—A type of kinetic energy that includes light rays, X-rays, radio waves, microwaves, and any other part of the electromagnetic spectrum. Electromagnetic waves are a result of the vibration of charged particles such as electrons. Microwave ovens use radiant energy to heat food by causing the water molecules in the food to vibrate.

Potential Energy is energy that is stored. In the example above, before it fell on your foot, the raised brick had potential energy because of its position. When it fell, this energy was converted to kinetic energy of motion.

Here are the main types of potential energy:

• Chemical Energy—Chemical bonds hold atoms together. It takes energy to break these bonds, and energy is released when new bonds form.
• Mechanical Energy—Examples include a clock that is powered by a wound-up spring, or an arrow shot from a bow. With this type, energy is stored in the mechanical device by the application of a force, such as when we wind the clock or pull the bow back.
• Nuclear Energy—When the nucleus of an atom splits or is fused to another nucleus, energy can be released. It is the type of energy that powers our sun and is found in nuclear power plants.
• Gravitational Energy—This is the energy associated with an object’s position in a gravitational field. A ball resting at the top of a ramp has higher potential energy than when it has rolled to the bottom. Water behind a dam has higher potential energy than when it has flowed to the river below. In each case the potential energy is due to relative position in the gravitational field.

You will be provided with a number of toys and other common household objects. The objects can include a flashlight, a clock with a “glow in the dark” face, a small mechanical toy, a drinking bird, a light stick, a hand-warmer or emergency cold packs, poppers, or a music box, among others. Your teacher may ask you to bring in a household object that involves energy.

For each of four objects, operate the device and write a complete description about what you observe. Be sure to include details such as sounds, movements, timing, and any changes you notice. If you are unclear about how to operate any of the objects, ask your teacher to show you how. Your teacher may choose to demonstrate some of the examples for the entire class.

To analyze what you saw for each of the objects, you need to consider what kinds of energy were involved. Using the types of energy listed in the Preparing to Investigate section on page 10, list all the kinds of energy you believe are involved in the operation of each of the objects. Your teacher may ask you to work in small, collaborative groups to complete this section.

Although some of the toys or objects may have appeared to “run out” of energy, one of the basic rules of science is that energy cannot be created or destroyed. It only changes from one form to another. Think back to your observations and analysis of the household items and speculate about how energy changed in each of the objects. In some cases there may have been multiple transitions.

1. How did you detect the types of energy you observed in thi 1. s investigation? Which types did you feel? Which types did you hear? Which types did you see? List any other ways you detected energy.
2. One definition of energy given in this lab was “energy is the ability to do work.” Considering all the objects you observed in this lab, record any examples of work that was done.
3. Given the definition of force (an influence that can cause an object to move or stop moving) identify some examples of where force was applied in this investigation.
4. Based on your experience, write a definition of energy in your own words. Also include some examples of things that are NOT energy.
5. Starting with the sun and ending with you making a piece of toast at home, write down as many types of energy and energy transitions as you can that go into your ability to have a piece of bread and toast it.
6. Often when the word “energy” is used, it refers to commercial production to help power our homes. List the major types of energy used in commercial power plants.

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