Bernoulli Effedt

The Bernoulli effect describes the fact that the pressure of a gas or liquid decreases as the gas or liquid flows more quickly. This means that if air flows above and below a flat object at different speeds, the slow-moving air will exert more pressure than the faster-moving air so that the object will be pushed toward the fast-moving air. Airplane wings are shaped so that air moves faster across the top of the wing than under the bottom. Thus the airplane is pushed upward, an effect, which is known as lift. The lift on a small plane is strong enough so that pilots must often point the nose of the plane downwards in order to maintain level flight. If the plane slows down to a certain speed known as stall speed, the Bernoulli effect can no longer provide enough lift to keep the plane air- borne.

Indy cars are shaped like upside down wings so that air passes more rapidly under the car than above it, and the car is forced down onto the track. Indy cars also use wings mounted behind the car and small wings on the front of the car. Early racecars traveled slowly enough so that they had no tendency to take off. As racing speeds increased, the Bernoulli effect became more important since the difference in the speed of the air above and below the cars increased. Modern chassis are carefully designed and adjusted during testing to allow the car to travel at maxi- mum speed without danger of becoming airborne.

The Bernoulli effect alone can provide enough lift to allow small planes to take off, but aircraft also use another effect to climb rapidly. They tip their wings so that their angle of attack pushes air downwards. The air in turn pushes up on the plane helping the plane take off. Similarly, the wing on the rear of a racecar uses the angle of attack to push air up so that the air in turn pushes down on the car. Too steep an angle of attack tends to slow the car down. As the wing pushes air for- ward, the air pushes back on the car. Thus, very careful adjustments are needed to obtain maximum performance during the Indianapolis 500.

A second consideration in the design of racecars is streamlining their design so that air flows around the car without turbulence. Turbulence changes the direction of airflow and slows the car down. It also destroys the operation of the Bernoulli effect. As racecars evolved and engines became more powerful, bodies had to be redesigned to streamline them and allow higher speeds.

Umbrellas turn inside out on windy days because the air under the umbrella is still and exerts more pressure than the fast-moving air above the umbrella, turning the umbrella inside out.

Full skirts blow up on windy days because the slow-moving air under the skirt exerts more pressure than the fast-moving air above the skirt, causing it to lift.

The air under a Frisbee moves more slowly than the air over the top. The pressure difference lifts the Frisbee.

A curve ball curves because it is spinning so that air on one side of the ball is traveling faster than the air on the other. This forces the ball to curve in the direction of the faster moving air.