Created by Dale Olive and Randy Scoville
Future Flight Hawai`i instructors
Demonstration at a glance:
A "volunteer" is asked to come up to test his lung capacity against the champion "iron man" science teacher. The volunteer gives one or two blows into the Bernoulli bag where his air is trapped and squeezed to the bottom to measure its volume. After the air is released, the science teacher holds the bag to his mouth and fills it with a single breath.
Bernoulli bags can be ordered from any science supply company or in a pinch I've used plain ole garbage bags. The "Volunteer" will probably do just as told and hold the bag right against his mouth - be sure he does! The eventual champion will need to hold the bag about six inches from his mouth and blow a stream of air into the bag in order to fill it.
This one is explained by the Bernoulli principle too. The faster a fluid moves the lower the pressure it creates. When the "volunteer" blows into the bag all he traps is his lung capacity. By holding the bag away from your mouth by six inches you create a narrow stream of air which according to Bernoulli is under lower pressure than the air around it because of its speed. Air from around the opening is under higher pressure than the air being blown in and so is forced in with that air. With some practice you can fill the bag with a single breath.
The fact that moving air creates lower pressure can be demonstrated by holding a one inch by 11 inch piece of paper just under your bottom lip and blow. The paper should rise upwards as you blow across the top of it.
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.