Chapter 5.2 Notes Bernoulli’s Principle

Bernoulli’s Principle says that as the velocity of a fluid (such as air) increases, the pressure in the fluid decreases. Water flowing in a stream speeds up when it passes through the narrow part.

Bernoulli’s Demo

Since the speed increases, the kinetic energy increases also. As the velocity of the fluid increases, the pressure of the fluid decreases.

The lifting force of an airplane is an application of Bernoulli’s principle. Air flows in two parts over a wing. One part flows over the top surface and the other flows along the bottom surface.

Air flowing over the top of the wing travels farther than the air on the bottom in the same amount of time.

This means the speed of the air above the wing is much faster than the speed below. The difference in speed leads to a greater pressure over the top of the wing and a lower pressure below the wing. This pressure difference is what causes the lift.

Airplanes

Physics of a Frisbee

Once in the air, lift and angular momentum act on the Frisbee. Lift is generated by the Frisbee's shaped surfaces as it passes through the air. Angular Momentum (spinning) is what stabilizes the Frisbee.

The air moving over the top of the Frisbee flows faster than the air moving underneath it. When there is lower air pressure on top of the Frisbee than beneath it, the difference in pressure causes the Frisbee to rise or lift.

Foam Frisbees

Physics of a Kite

Bowing is a smooth curve often at the center of the kite. It helps the kite catch the wind, like a parachute does. It can increase lift, due to Bernoulli’s Principle.

Having too much of a bow might trap wind and create too much drag, or provide too much weight. Having too little will cause a kite to act as if there is none, so the Pressure difference between the top and bottom of the kite is not very different. Remember, the pressure difference causes the Lift.