Bernoulli effects

Each of these simple investigations illustrates how Bernoulli’s principle applies to moving air. Bernoulli’s principle states that the pressure of a fluid decreases as its velocity increases.

For each investigation completed:

(a) Record your observations.

(b) Explain your observations in terms of Bernoulli’s principle, as follows — look for areas of fast moving air (low pressure) and slower moving or not moving air (normal air pressure).

1. Place a table tennis ball inside a small clean funnel. Point the funnel upwards and attempt to blow the ball out of the funnel.

2. Attach two short lengths of cotton to two table tennis balls using sticky tape. Tie the pieces of cotton to a pencil so that the balls hang down level and are a few centimetres apart. Using a straw, blow a stream of air through the gap and observe what happens.

3. Place two paper or cardboard tubes side by side on the desk, with a small gap between them. Using a straw, blow a stream of air through the gap and observe what happens.

4. Set an empty vacuum cleaner to blow air out. Suspend a table tennis ball in the airflow from the vacuum cleaner nozzle and turn the vacuum cleaner on. Change the angle of the nozzle and keep the ball suspended.

5. Hold a sheet of paper in both hands, using the thumb and first finger of each hand. Allow the paper to flap over and away from you, forming a curved surface like a wing aerofoil. Blow over the surface of the paper and observe what happens.