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Bernoulli's Law

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Look at the large bar (labeled “TELMEX”) across the back of this racecar. The bar is called a spoiler. It causes air pressure to push the car toward the ground. This increases friction between the wheels and the pavement, helping the car to hug the track. How does a spoiler work? Bernoulli’s law has the answer.

What Is Bernoulli’s Law?

Bernoulli’s law states that the pressure of a moving fluid such as air is less when the fluid is moving faster. Pressure is the amount of force applied per given area. The law is named for Daniel Bernoulli, a Swiss mathematician who discovered it during the 1700s. Bernoulli used mathematics to arrive at his law. For an animation of the law, go to the URL below.

http://mitchellscience.com/bernoulli_principle_animation

Using Air Pressure to Fly

Did you ever wonder how the wings of airplanes or birds allow them to fly? Bernoulli’s law provides the answer. Look at the wings of the plane and hawk in the Figure below . The shape of the wings causes air to flow more slowly below them than above them. This causes air pressure to be greater below the wings than above them. The difference in air pressure lifts the plane or bird above the ground.

Airplanes and birds fly using Bernoulli's law

Q : How does a spoiler on a racecar use Bernoulli’s law?

A : A spoiler on a racecar is like an upside-down wing. Its shape causes air to flow more slowly—and air pressure to be greater—above the spoiler than below it. As a result, air pressure pushes the car downward, helping it to stay on the track.

Summary

  • Bernoulli’s law states that the pressure of a moving fluid such as air is less when the fluid is moving faster.
  • Bernoulli’s law explains how wings of airplanes and birds create lift and allow them to fly.

Vocabulary

  • Bernoulli’s law : Law stating that pressure in a moving fluid is less when the fluid is moving faster.

Practice

Use Bernoulli’s law to explain what you observe in the demonstrations at this URL:

http://www.youtube.com/watch?v=P-xNXrELCmU

Review

  1. What is Bernoulli’s law?
  2. Explain how the wings of an airplane create lift that allows the plane to leave the ground.

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