Question

Suppose a drinking straw is in a glass of water. Someone blows air across the top of the straw.

Answer 1

What are you trying to ask?

Answer 2

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. Instead of putting the straw inside your lips, blow across the top of it. You don't want to blow into the straw. Instead, your breath should go straight across the top. 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 starts. 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 is 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.

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.


Its an experiment