You are going to watch three demonstrations that were carried out by scientists to show that air has pressure.

Watch each demonstration and answer the questions.

1 The Magdeburg hemispheres
In 1657 one of the burgomasters of Magdeburg who was a scientist made a large version of these hemispheres. Two teams of eight horses tried, and failed, to pull them apart.
Before the air is pumped out, do the hemispheres stick together when the two halves are joined?
On the diagrams on the Resource sheet, draw arrows to show the force of the air before the pump is switched on and after the air has been pumped out.
Label the space where there is no air with the scientific word for an empty space.
What happened when the handles were pulled?
What happened when the tap was opened?
What does this experiment tell us about air pressure?
Imagine you were a newspaper reporter at the time of the original experiment. Write a paragraph about the experiment and what it showed.
2 The collapsing can
What happens as the air is pumped out of the can?
On the Resource sheet, draw arrows on the can before air is pumped out to show the force of the air. Draw the can after air has been pumped out. / Why doesn't the can go back to its original shape when the air goes back in?
3 The barometer
The first barometer to measure air pressure and forecast the weather was made in 1643 by Evangelista Torricelli.
What happened when the tube of water was inverted?
Why didn't the water run out of the tube?
On the diagrams mark the height of the liquid in the water barometer and the mercury barometer.
Why is mercury used in barometers?
What will happen to the height of the liquid in the tube if the air pressure a rises or b falls?
Torricelli made a water barometer. The top of it came out above the roof of his house. He noticed that on fine, clear days the water level came up above the roof of his house and on wet stormy days the level dropped below the roof and could not be seen from outside. He floated a little model man on the surface of the water. People came to look at his house and see if the little man was outside – forecasting good weather – or inside because bad weather was on the way.
Draw some cartoon diagrams telling the story of Torricelli's water barometer for forecasting weather.

© Harcourt Education Ltd 2004 Catalyst 3

This worksheet may have been altered from the original on the CD-ROM.