Sponsored by Hawai`i Space Grant Consortium, Hawai`i Institute of Geophysics and Planetology, University of Hawaii, 2001

BULL ROARER
Created by Dale Olive and Randy Scoville
Future Flight Hawai`i instructors

Demonstration at a glance:
A twirling piece of wood on a string emits a sound as it is twirled overhead.

Set-up:
Obtain a piece of wood from the hardware store with the same dimensions as a ruler or slightly larger. Cut off a piece about 18 inches long and drilled a hole one inch from its end. Tie a piece of string about 2 feet long to the wood through the hole. To get it vibrating I sometimes twirl the string before I swing it overhead.

Theory:
Try to have the kids guess how the device is actually making sound. If you slow down the swing, the kids can actually see the wood spinning very fast. It is this motion which is vibrating the air causing the sound.

Extension:
The students may have seen this done in the movie "Crocodile Dundee" where he uses a device like this to call bats. I'm not sure if it calls bats or not but it does make an eerie sound. I've made some bull roarer's that are three feet long but the amount of force on your hand as you twirl it is harsh. I also don't like swinging it towards an audience in case the string breaks so keeping something that long off the ground is tough too. The sound generated by the large ones is deeper and louder. You could try different shapes, different lengths of rope etc... to see if the pitch and volume change.


Index of Activities.

http://www.soest.hawaii.edu/spacegrant/ScienceDemos/
Communications: Hawaii Space Grant Office
This activity is featured in Future Flight Hawaii, a K-12 Education Project of Hawaii Space Grant Consortium.
FEB 27 2001.