The Straw Trombone

You will need:

a drinking straw
a tall glass of water or some other liquid

What to do:

Put the straw into the glass of water.
Hold the glass in one hand and the straw in your other hand.
Holding the straw flat against the side of the glass, bring it up to your lips, just as if you were going to drink.
Now instead of putting the straw into your mouth, blow across the top of it. As you blow, move the straw back and forth, up and down slightly. When you get the angle just right, you will hear a whistling sound. This may be very faint, but with practice, you can get a very loud, clear whistle.
Once you get the straw to whistle, the fun begins! As you are blowing, keep the straw still, but move the glass of water slowly downwards. As the glass moves down, the tone of the whistle changes. Move the glass upwards and the tone changes again.

What’s going on?

When you blow across the top of the straw, you cause the air inside the straw to vibrate. This vibration causes the sound that you hear. By changing the length of the column of vibrating air, you change the sound. The longer the column of air, the lower the pitch. The shorter the column of air, the higher the pitch.

Why would moving the glass up and down change the length of the column of air? The water inside the straw will move to the same level as the water outside the straw. As you move the glass downwards, more of the straw is above the water level, so the length of straw that contains air is longer. When you move the straw downwards, more water moves into the straw and the length of the straw that is filled with air is shorter. So what are you waiting for? A one, a two, a one two three four….