Robert Krampf’s Experiment of the Week:  THE BULLROARER

This week’s experiment is an old one, but a fun one. The basic concept of the Bullroarer can be found in the distant history of Europe, Asia, Africa, the Americas, and Australia.

While it is traditionally made of a flat piece of wood, this version is very quick, easy to make, and produces a similar sound. To try it, you will need:

• a plastic spoon
• a rubber band large enough to stretch around the spoon lengthwise
• 2 or 3 feet of strong string

Tie one end of the string to the rubber band. Then stretch the rubber band around the spoon. Be sure to use a plastic spoon, not a metal one! If the spoon goes flying, you want to be sure it won’t cause injury or damage. Be sure to watch the bloopers at the end of the video.

Make sure you have plenty of space, so you don’t whack a lamp, the cat, or your little brother. (I know it’s tempting, but it would be wrong.) Hold the string about two feet from the spoon, and start swinging it in a circle. Start swinging slowly, and then gradually speed things up until you get a nice sound. If you don’t get much sound, reverse the direction of the spin, or try adjusting the rubber band. It does not take long to get a nice, loud, humming sound.

Why? As the spoon and rubber band move through the air, it causes the rubber band to vibrate. That causes the air around it to vibrate, and that vibration in the air is what we hear as sound.

You can alter the sound by changing how fast the rubber band vibrates. Making the rubber band tighter, or spinning it faster, will cause faster vibration and a higher pitched sound. Making the rubber band looser, or spinning it slower, will cause slower vibration and a lower pitched sound.

There is plenty of room for experimentation with this. Try different rubber bands. Try using more than one at a time. Try using a plastic fork instead. The more you experiment, the more you will learn, and the more fun you will have.

Have a wonder-filled week.

Reprinted with permission. © 2009. Robert Krampf’s Science Education