Materials

1. Five identical plastic bottles
2. Water

Procedure

1. Fill five identical plastic bottles with varying amounts of water.
2. Arrange the bottles in order from most to least full.
3. Blow across the top of each bottle and compare the different sounds you make.

What's Going On?

Changing the amounts of air and water in the bottles lets you change the pitch (how high or low the sound is). When you blow across the tops of the bottles, you are making the air inside vibrate. In bottles with more air, vibrations are slower, so the pitch is lower.