Explore: Bernoulli Brainteaser

Lift comes from faster moving air producing a region of low pressure.  This can happen when air flows between two objects, or when it is flowing over certain shapes (such as a wing).  Understanding how Bernoulli’s Principle works requires you to consider where the air is high pressure and where the air is low pressure.  The high pressure areas always push into the lower pressure ones.

Take a sheet of paper and place it on top of two stacks of books leaving some space between the books (see diagram).  Blow under the paper and observe what happens. Can Bernoulli’s Principle explain what happened?

Blowing under the sheet of paper produces an area of faster moving air.

Faster moving air = lower pressure

This means the air on top of the paper had a higher pressure.  As a result, the higher pressure air on top of the paper PUSHES the paper DOWN into the lower pressure area.  In this case, the lift is actually pushing downwards – similar to how a car spoiler works, to keep a race car flat on the track when it is going very fast.

See if you can use Bernoulli's Principle to explain other brainteasers you will be trying! Remember to think of where the air is moving faster and where the air pressure is slower. This should give you an idea of where the lift will be produced.

  Notebook: How can we show Bernoulli's Principle at work?

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  Check Your Answers

Activity

What Happened?
Blowing on Paper
 The sheet of paper moved up.
Paper Strips The paper strips moved together.
Ball Balancer The ping-pong ball stayed floating above the hair dryer.

Activity

What Happened?

Can you explain what happened using Bernoulli’s Principle?
Blowing on Paper
 Answers will vary The air flowing over top of the paper was moving faster and with lower pressure. The higher pressure air under the paper pushed it upwards.
Paper Strips Answers will vary The air flowing between the sheets of paper was moving faster and with lower pressure. The higher pressure air on the outside of the sheets pushed them inwards.
Ball Balancer Answers will vary. The air flowing past the ping-pong ball was moving faster and with lower pressure. The higher pressure air surrounding the ping-pong ball holds it in place in the air stream.