This experiment is a super easy demonstration of the effects of air pressure and had my 6 year old in fits of giggles for a long time.
What you need:
An empty squash bottle.
A small rolled up ball of paper, small enough to sit inside the mouth of the bottle.
- Place the bottle on the edge of a table and put the ball of paper inside.
- Try to blow the paper into the bottle.
- It should shoot back out towards you.
Why does it do that?
The same principles that keep aeroplanes in the sky also apply to this neat little experiment. The key point is that moving air is at a lower pressure than still air. This is the Bernoulli Principle. In the case of the squash bottle the air that is blown towards the mouth is deflected around the the sides of the bottle (very little moves past the piece of paper). This means that the air pressure in front of the ball of paper is lower than behind, and so the paper flies out.
Aeroplane wings are specially shaped so that air travels faster over the top of the wing than over the bottom surface. Again the pressure is lower above than below and the wing is “pushed” upward by the higher pressure air – called lift. The faster the plane moves forward the bigger the lift it experiences.