Daniel Bernoulli was a Swiss scientist of the 18th Century. After many years of research into pressure and fluids, he concluded that:
The pressure in a fluid decreases as the speed of the fluid increases
This applies equally to liquids and gases. This is known as the Bernoulli principle and there are a few experiments and demonstrations that can be conducted in schools to demonstrate it.
Experiment one
This involves taking a sheet of A4 paper, holding it at one end by the corners and placing it level with your mouth. If you blow over the top surface of the paper it should rise. This happens because the moving air which is travelling across the top of the paper is of lower pressure than the air beneath. It shows how aircraft wings work by gaining 'lift' from the difference in pressure above and below the wing.
Experiment two
A large funnel and table tennis ball are required for this demonstration. The ball is placed into the funnel and the mouth of the funnel is placed to your lips. (you will need to tilt your head backwards to achieve this) Blow hard but consistently into the funnel and at the same time tilt the funnel as if you are pouring the ball out. The ball should stay inside the funnel. In this case the ball stays in place because it is attracted to the area of lower pressure created by blowing air along the sides of the funnel.
Experiment three
This requires a table tennis ball, a hairdryer and a cardboard tube which the ball can fit through. The hairdryer is pointed towards the ceiling and turned on. The ball is placed in the air stream from the hairdryer. The ball should 'hover' in the stream quite comfortably. The hairdryer may even be tilted slightly showing the ball is being held firmly in place by the area of lower pressure (the moving air) If the cardboard tube is held above the ball, the ball should be sucked up into the tube. This happens because adding the tube makes the air move into a narrower space which means it gains speed, creating even lower pressure and causing the ball to more upwards.
The Bernoulli effect can be witnessed by observing the soft top of a convertible car travelling on a motorway. The difference in pressure makes the roof bulge upwards towards the area of lower pressure.
Tennis, baseball and football players all use the Bernoulli principle to effectively bend the trajectory of a ball by spinning it a certain way.