This Week's Experiment - #271 Grass Whistle

a blade of grass. You can also use a thin strip of paper, but grass works better.

Pick a blade of grass that is about as long as your first finger. Look for one that is wide, without any tears or holes. While you are searching, take a few minutes to really look at the ground. You may see all sorts of plants, insects and other living things that you never noticed before.

Once you have a nice blade of grass, you are ready. Hold your left hand up in front of you. Make a loose fist, with your thumb pointing upwards and your thumbnail towards you. With your right hand, put the blade of grass along the right side of your thumb. Then bring your right thumb up beside your left, so that the grass is trapped between your thumbs.

You should notice that between the first and second joints of your thumb there is a gap where the grass is not touching either thumb. Be sure that the grass is stretched tightly in this gap. Then put your thumbs to your mouth, so that this gap is against your lips. Purse your lips, as if you were going to blow out a candle and then blow hard. If you do it just right, you will be rewarded by a loud sound. Depending on the shape of the blade of grass, how tight it is, and how hard you blow, you may get anything from a low rasp to a loud, shrill whistle. With some practice, you can make quite a variety of sounds.

Why would blowing on a blade of grass make this sound? Blow again and pay attention to what you feel, not just what you hear. You should feel the grass vibrating. As you blow across it, it flutters back and forth, almost like a flag fluttering in the wind. The tighter it is stretched; the higher the pitch will be. You can alter this by flexing your thumbs.

As we have seen in the past, vibration can cause sounds. The grass vibrates, which causes the air around it to vibrate. These vibrations are carried through the air to your ears, where you hear them as sound.

Now you have an excuse to make lots of annoying sounds, all in the name of science. Just don't get too annoying or you might wind up cutting the grass to prevent further exploration. If you dislike mowing grass as much as I do that should be enough to make sure you are not too noisy.

From Robert Krampf's Science Education Company
PO Box 60982
Jacksonville, FL 32236-0982
904-388-6381
krampf@aol.com

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