Students suspend an object in the air by blowing down on it.
Students explore the Bernoulli Principle.
Bernoulli Principle, air pressure
large wooden or plastic thread spools, index cards trimmed to 3 by 3 inches, pushpins, 2-inch sections of drinking straws (optional)
Provide each student or group of students with a spool, an index card, and a pushpin. If students are working in groups, also provide each student with a 2-inch piece of a drinking straw.
Have students hold a card against the bottom of a spool with the pushpin sticking into the spool's hole and blow strongly through the hole in the top of the spool as they let go of the card. (If the card falls at first, experiment with different sized cards or spools until the card hangs suspended beneath the spool.)
Discuss with students why the card could be suspended by blowing down on it. (When a person blows into the spool, the air hits the card and accelerates outward. As the air accelerates, its pressure drops. The air rushing between the spool and the card exerts less pressure on the card than does the still air underneath the card. The still air pushes the card toward the spool and holds the card up against gravity.)
Note: The entire experiment, including explanations and a more involved version, can be found at the Bernoulli Levitator site.
Assessment Evaluate students on their participation in a discussion following the experiment.
Lesson Plan Source
Science Snacks Online from The Exploratorium