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When students visit the BIG Little Science Centre, they spend most of their visit doing ‘hands-on’ science in our two hands-on rooms. However, we usually introduce ourselves to new groups by doing a series of entertaining and educational demonstrations for them. (This way, we big kids get to have some fun, too!) In the next few issues, the editor will describe

some of our favourite demonstrations, beginning with the topic of Air Pressure. Most of these ideas come from sources long forgotten, but some of them are original with the BIG Little Science Centre. As a rule, we try to take an old, well known demonstration and put our own spin on it.

Air Pressure 1

What do we mean by pressure?

Place a balloon on top of the 'Bed of Nails'. (Left photo) Put the cover on top of the balloon and push down (gently). The balloon will not burst because the force you exert is spread over many nails. Pressure is a measure of the force on a unit area of surface.

Now replace the bed of nails with a single nail. All the force will be concentrated on the small area of the tip of one nail. Pressure is much greater! Push down gently on the cover and "Bang!"

Toilet Plunger

Push a (clean and new) toilet plunger hard into the blackboard so that it sticks to the board. What is keeping it there? (Several plungers can be used at once.) Most of the air from under the cup is pushed out, so the pressure in the space between the rubber cup and the board is close to zero. Air pressure outside the cup is what keeps the plunger 'stuck to the wall'.

‘Atmospheric Pressure Cups’ *

Hold two of the black rubber cups facing the audience and show that there is no 'glue' or other substance on them. Push two of the cups together so that all the air is squeezed out between them. Now ask a young volunteer (or two) to pull the cups apart.

*These provide an affordable alternative to Magdeburg Hemispheres or Plates.