F5-41: WIND BAG

ID Code: F5-41
Purpose: Demonstrate entrainment
Description: Unroll a five-foot section of thin plastic tubing, about six inches in diameter, and tie off one end, forming a long "balloon." It takes about eight or ten lungfulls of air to completely fill it with air, blowing it up like you would blow up a balloon. Now squash the balloon as it lies flat on the table, removing all the air, hold the open end about five or six inches from your mouth, and blow a lungfull of air sharply into the balloon. It will fill up entirely with ONE lungfull of air. When you blow into the balloon, you form a very rapidly moving airstream. Air from the atmosphere surrounding your airstream becomes caught up in the airstream, multiplying by severalfold the amount of air that is being pushed into the balloon. This process is called entrainment. Note that although this phenomenon is often attributed to the Bernoulli effect, it is not. The Bernoulli effect deals with isentropic flow along streamlines, within which realm this demonstration does not fit.
Availability: Available