# Bernoulli’s Principle

Q:
I need to know about the Bernoulli’s principle also need to know about physics
- Breanna gallagher (age 13)
hood river OR U.S.A
A:
Hi Breanna,

There is already a good response to the question "What is physics?" on the Physics Van webpage. If you look through our answers collection it is under the "Everything else" section.

Bernoulli’s Principle says that when liquids or gases move at a faster speed, they have less pressure. This means that faster moving liquid or gas doesn’t push as much as slow moving liquid/gas on the stuff that’s surrounding it. To see this at work, find something like a leaf blower or a vacuum cleaner that can run in reverse and can blow air out. When you turn it on, you will get a stream of air that comes out the nozzle at a fairly fast speed. Now find a light ball; something like a ping-pong ball works pretty well. Place the ball above the nozzle and in the air stream (nozzle pointing up), and you will see that instead of being pushed away and knocked to the ground, the ball will stay in the air stream. This is because according to Bernoulli’s Principle, the air that isn’t moving that surrounds the air stream is at a higher pressure than the moving air, so it pushes on the ball and keeps it in the air stream. The ball is fairly stable floating above the nozzle, and you can actually tilt the nozzle slightly without the ball falling out.

(published on 10/22/2007)

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