Materials List: equal-sized cardboard squares with holes (paper-punch size) in the center, modeling clay, flashlights, string
Light and sound both travel in waves. Light does not need air to travel. It can pass through empty space where there is nothing to carry it. Light waves travel in straight lines, but they travel so fast we can’t see them move. We see light waves as a straight, steady beam of light. Light travels much faster than sound, so we see light almost in the same second that it is made.
Class Discussion: Ask “Since light and sound both travel as waves, do you think they travel at the same speed?” Facilitate a discussion. As the discussion progresses, have students think about
· Thunderstorms – what comes first, thunder or lightning?
· Fireworks Displays – does the “boom” happen at the same time as the lights?
· Baseball Games – do you hear the sound of the ball hitting the bat at the same time you see the ball go into the air?
Investigation Task: Explain to the students that they will be investigating how light travels in straight lines. Divide the class into groups. Each group will need 3 cards with holes in the center, some string, modeling clay and a flashlight. Describe the following procedure (you may want to put it on the board or a chart) and have students engage in the task. Remind students of safety issues of looking directly into a beam of light.
1. Use lumps of clay (one on each side of card) to stand the cards up so that all the holes are in a straight line.
2. Check that the holes are lined up by passing a length of string through the holes.
3. Take the string out. Look to see if you can see through the three holes.
4. Wait for the lights to be turned off.
5. Place the flashlight against the first piece of cardboard and shine it through the first hole. Look at the card farthest away from the flashlight. You should be able to see the light shining through.
6. Move the middle card about one inch to the left. What happens to the ray of light now?
Observe students as they work to complete the investigation. When appropriate, ask students to explain what happens when the middle card gets moved. Once all students have completed the investigation, facilitate a group discussion of what happened during the investigation and why.
See book, Sound and Light, in Resources section.