Science of Sound!

Here's what you'll need...
  • glass soda bottle
  • Water
  • Breath
  • Spoon

Have you ever made an instrument from a glass bottle? It is great isn’t it? It’s the easiest instrument to make and play with! All you need to do is obtain a glass soda bottle and put a little water in it. Then you can blow across the top and if you blow just right it will sing! Then you can use a spoon or something to lightly tap the bottle and it will also make a sound. In order to change the pitch just add or remove water from the bottle.

Now compare the two ways of making sounds(blowing and tapping). How does the pitch change when you change the water? The sound seems to become lower in pitch the less water there is in the bottle when you blow over the top, however the pitch seems to rise when you do the same thing except with tapping. This is where things get crazy!

Sound is created when something vibrates. The bigger that something is the lower the pitch will be. Now we need to figure out what is vibrating. When we blow over the top of the bottle the air inside of the bottle vibrates and that is what gives us our pitch. Naturally when there is less water in the bottle there is more air in the bottle meaning the pitch will be lower.

The tapping is the harder part. Think about what could possibly be vibrating when you tap it? The only good conclusion that would explain the pitch change is the water itself! When there is less water the pitch is higher and when there is more water the pitch drops which is the opposite as when we blow into the bottles!

If you have multiple bottles then you can make a song by having different bottles at different pitches. For Mary Had a Little Lamb you will need four bottles. Fill them up to about the following measurements: 8 cm, 5.5 cm, 4 cm, and 3 cm. Don’t stop there! See if you can come up with other songs!