Observing Sound Waves

Objectives

• Students will use observation skills to draw conclusions and make predictions.
• Students will be able to see sound waves.

Materials

• Empty soup can
• Can opener
• Large balloon
• Flashlight
• Small mirror (from a compact)
• Scissors
• Rubber band
• Glue
• Journal

Procedure

Imagine what happens when you drop a stone into a pool of water. Waves ripple out from the spot where the stone entered the water. Those water waves are similar to how sound waves travel through the air.

When you speak or shout, your vocal chords vibrate. These vibrations go out in all directions through the air as waves. When the waves reach our ears, they make our eardrums vibrate too, so we can hear the words.

But to get to our ears, sound waves need to travel through some stuff, like air, that can vibrate. Air is made up of particles, and these are what move to make the sound waves. The vibrating object, like your vocal chords, bumps the air particles next to it. They then bump the particles next to them, and so on.

Most of the sounds we hear travel through the air, but sound waves can also move through water, wood, and metal. You can test this out for yourself. All these things have particles that can vibrate. But if there's no particles, there's nothing to bump into, so sounds can't travel.

In outer space, there are no particles to bump into, so sounds can't travel. No particles means no vibrations, and no vibrations means no sound waves, which means no sounds.

In movies and on TV, you'll sometimes see and hear things exploding in outer space -- alien spacecraft and things like that. The explosions can make the story more exciting, but in real life, you wouldn't be able to hear an explosion in outer space.

Instructions for the Project:

1. Remove both ends of the soup can with the can opener, and carefully remove any sharp edges.

2. Cut the balloon so that it has a large, flat surface area and stretch the balloon around one end of the soup can. Secure the balloon with the rubber band.

3. Glue a small mirror (like a mirror from a makeup compact) to the center of the stretched balloon. Be sure that the reflective side is facing up.

4. Place the can on a table and secure it so that it doesn't roll away.

5. Turn the lights out and shine the flashlight onto the mirror at an angle so that the light bounces off the mirror and reflects on the wall.

6. Clap your hands next to the open end of the soup can. What happens to the reflection on the wall? Write down your observations in your journal.

7. Shout into the open end of the can. What happens? Write your observations.