BERNOULLI HEAD LICE DETECTOR
Created by Dale Olive and Randy Scoville
Future Flight Hawai`i instructors
Demonstration at a glance:
A hose is twirled emitting a high pitch sound . . .head lice detected! Once the "volunteer" is chosen the detector is twirled over their head to remove the lice.
Obtain a Bernoulli hose from a scientific catalog or toyshop. While distracting the "volunteer" with questions about head lice, place a small pile of cut paper on top of their head. Twirl the hose over their head with the end placed right over the pile of paper. This will suck it up and shoot it out the other end.
The sound comes from the fact that the ribs in the hose are vibrating air. One question you could ask "is the air being vibrated by the ribs on the outside or inside of the hose?" The fact that the pile of cut paper is picked up by the hose tells you the sound is coming from the air being sucked up into the tube. Why is it sucked up? It's explained by the Bernoulli principle. Bernoulli stated that the faster a fluid (air is a fluid) moves the lower the pressure it creates. The faster air moving over the top of an airplane wing allows it to remain in the air due to the higher pressure on the bottom pushing the wing upwards. In this demonstration, the end of the twirling tube is moving faster and thus creates lower pressure on that end. The higher pressure on the still end forces air up into the tube.
There are many Bernoulli demonstrations that can be done to reinforce this concept. One similar to the one above is the straw atomizer. Cut a straw 3/4 of the way through about three inches from the top and bend it 90 degrees. Place the long end into a cup of water. Cut the bottom of the straw off so that the bend is no more than about one inch above the water. While keeping the straw at 90 degrees, blow steadily through it. The air moving over the bent straw going into the water should lift the water up and out much like an air brush or perfume atomizer does in a fine spray. Again, this is Bernoulli. The fast moving air over the straw creates lower pressure and the higher pressure on the water pushes it up the straw and out.
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.