Quick Science: Bernoulli’s Principle #1

It’s April, almost May. Need a quick activity to punch up the enthusiasm in your science class? This activity could be part of a weather unit with air and wind. It could be added to a physics unit about force and air pressure. It’s a great demonstration that students can share with family members at a science night or open house.

Â

Turn on the hair dryer and aim the flow of air up. Carefully balance a ping-pong ball in the stream of air. Gently tilt the hair dryer. How far can you tilt the hair dryer before the ball falls out of the stream of air?

EXPLAIN that the air from the hair dryer is moving at higher speed than the room air. The air moves around the ball to create a pocket of low air pressure. When the ball moves to the side of this pocket, it will be pushed back in by the higher pressure room air. The upward force from the air stream keeps the ball aloft. A diagram of the activity can be shown to students.

Click here for a more in-depth explanation from The Exploratorium.

What if you use a leaf blower? Steven Rokusek at South Dakota Public Broadcasting did it both in studio and in a gym. Their resources include FREE lesson plans you could add to your resources. Check it out!

Another video to consider (maybe with the volume turned down so you can discuss as a group and then explain) uses both a ping pong ball and a balloon. The demonstrator blows gently on the ping pong ball knocking it out of the stream of air and the balloon continues to hover above the hair dryer.

Each student needs a ping pong ball and a straw. Instruct each child to lay on the floor with the ball above the straw as shown and exhale slowly. If there isn’t enough floor space or students might become disruptive, suggest they hold the ping pong ball on their fingertips like a baseball on a trophy.  When they exhale, they’ll see the ping pong ball will lift off from the straw slightly and hover above the straw. It’s odd to tilt your head back far enough to keep the straw vertical so you might splurge on flexible straws. Bend the straw in an “L” shape as you do the experiment.

EXPLAIN that the ball hovers above the straw because air pressure from the straw pushes up on the ball and the air flows around the ball to keep the ball in place.

Check out this other great resource: Fun with Bernoulli – American Society for Engineering Education