After sight, hearing is the most important of our five senses. Sound is caused by waves, and sounds are made by vibrating objects. Sounds can vary in two ways: amplitude and pitch. The amplitude of a wave tells us how much energy was used to produce it. The greater the amplitude, the greater the volume. Frequency is the number of waves or vibrations sent out in a specified amount of time; the faster something vibrates, the higher the pitch.
What You Need
- Small tin can with both ends removed
- Piece of rubber balloon
- Small mirror
- Rubber band
What to Do
- Stretch the balloon fragment tightly over one end of the can, using the rubber band to keep it in place.
- Glue the piece of mirror to the stretched balloon, slightly off-centre.
- Darken the classroom, and move the can near the blackboard.
- Hold it away from and at an angle to the blackboard.
- Shine the beam of light so that it strikes the mirror and rebounds onto the blackboard.
- Have someone speak, sing, shout, or (softly) blow a whistle, into the can.
- Observe the reflection that you now see on the blackboard.