4.33 Bernoulli’s Law
4.33 Bernoulli’s Law
- State Bernoulli’s law.
- Relate Bernoulli’s law to flight.
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 lawstates 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 theFigure4.65. 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.
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.