Author: Cindy

Think about this. Ella understands that light is a form of energy, but she is having trouble with the idea that light energy cannot be created or destroyed.

“Look,” she told her aunt, who is a science teacher. “When I flip the switch and turn off the lights, I cause all the lights in the room to go away.” She demonstrated and made the room very dark.

“Now look what happens when I turn the light switch back on. The room fills with light again. Didn’t I just create and destroy the light in the room?” she asked.

“No, you certainly did not,” her aunt said. “All you did was demonstrate how energy can change from one form into another.”

Let’s look at some examples of how energy changes from one form to another in this lesson.

German-born Albert Einstein was awarded the 1921 Nobel Price in Physics. His studies of light transformation helped to base his discovery of the photoelectric effect.

The Investigative Problems:

What are examples of energy?
Can one form of energy change into another form of energy?

Gather These Things:

1.5-vold dry cell
5-inch pieces of electric wire
Small wooden boards
Assorted rubber bands (different thicknesses, but same length)
1.5-volt light bulb
Sandpaper
Sturdy shoe box

Procedure & Observations

Electric energy ito light and head energy: Take a 1-5-volt dry cell, a five-inch wire, and a light bulb. Test different combinations until you get the light bulb to come on. Show your teacher when you are successful. Make a drawing to show how you connected everything.

Feel the light bulb. Can you tell if it has gotten any warmer? (Note: This is a small amount of head and it may not be easy to detect.)

Mechanical energy to heat energy: Rub a piece of sandpaper quickly over a board several times. Feel the sandpaper and the board. What kind of energy is produced?

Mechanical energy to sound energy: Remove the cover from a sturdy box and cut three groves on opposite edges of the box. Now choose three rubber bands of equal length, but each with a different thickness. Stretch the rubber bands around the box, fitting each into one of the grooves. Pluck each rubber band. Observe that it is vibrating. Listen for a sound. Repeat for each rubber band. Compare the pitch made by the different rubber bands. Record your observations.

The Science Stuff

Energy is what enables matter to move or to change. Energy is found in many different forms, such as heat, light, electricity, mechanical (the energy in moving things), sound, nuclear, and chemical. One form of energy can be changed into another form of energy. Still, the total amount of energy never changes. This means that energy cannot be created or destroyed. These ideas are expressed in one of the most important laws in all of science – the law of conservation of energy.

These activities illustrate some of the main forms of energy. Each activity shows one form of energy being changed into another form of energy. Electrical energy changed into light and heat, mechanical energy changed into heat, and mechanical energy changed into sound.

In the first activity, when the equipment was wired together correctly, an electric circuit was completed. An electric current then moved through the dry cell, wires, and light bulb. As the electric current moved through the light bulb, electric energy changed into light energy and heat energy.

This activity illustrates another important concept about energy. It shows that energy can be transferred from one place to another. Much of the earth’s energy is transferred from the sun to the earth.

Remember the conversation between Ella and her aunt? When Ella flipped the light switch, the electric current began to move through the wires and the light bulb. Inside the light bulb, electric energy changed into light and heat energy, which is the same thing that happened in your activity with electricity. When she turned the lights off, the objects in the room absorbed the heat and light energy. (This is a small amount of energy, and you probably couldn’t detect it without some sophisticated equipment.)

When you rubbed a board with sandpaper, your motion produced mechanical energy. This motion produced friction between the sandpaper and the wood, causing the molecules to move faster. As a result, both the sandpaper and the wood became hotter. Thus, the mechanical energy of the moving sandpaper changed into heat energy.

You were also the source of motion when you plucked the tight rubber bands, causing them to vibrate. Sound is produced when a force causes something to vibrate and produce sound waves. Sound energy is carried in waves.

Making Connections

Another way in which mechanical energy can produce sound waves is by tapping on a table. Tapping on the table causes the table to vibrate in the same way plucking on the rubber bands caused them to vibrate. Sound waves actually travel faster through the table than through the air. You can put your ear next to the table and hear the tapping sounds clearly. You can also raise your head and hear the sounds as the sound waves pass through the table and then through the air.

When electrical energy passes through a light bulb, it is changed into light energy and heat energy. Even though the heat energy is unwanted, it is still part of the electric bill. Engineers try to design light bulbs that increase the amount of light and decrease the amount of heat produced. Some progress has been made, but light bulbs continue to produce unwanted heat.

Dig Deeper

Start with the energy being given off from a TV or a radio in your home. Try to figure out where this energy comes from. See how far back you can trace the energy changes. This gets a little complicated, so get ad good reference book to help you.

What is the difference between an electric motor and an electric generator? They basically contain the same parts and are built the same way. However, an electric motor changes electric energy into mechanical energy, and an electric generator changes mechanical energy into electric energy.

In 1905, Albert Einstein proposed a theory that altered the law of conservation of energy. He said that matter can be changed into energy, and energy can be changed into matter, but the total amount of matter and energy in the universe remains the same. How was Einstein’s theory shown to be true?

What Did You Learn?

Give two examples of how one form of energy can change into heat energy. Give another example of an energy change.
List two ways in which energy does work for us.
The following list contains examples of forces, properties of matter, and forms of energy. Underline all the examples of forms of energy: inertia, heat, density, buoyancy, electricity, lift, weight, chemical, push, and nuclear.
Define mechanical energy and give an example.
What kind of energy can be quickly provided by a battery?
What is the law of conservation of energy?
Give an example of when an unwanted form of energy is produced in a device.
What happens to a roomful of light on a dark night with the lights are turned off?
Was energy transferred from the batter to the light bulb when an electric circuit was completed?