This week we tried an experiment which I had often heard of, but never attempted. It involves the rule "to every action there is an equal and opposite reaction"- other wise known as Newton's Third Law of Motion. Basically you fill about one fifth of a two litre bottle with water. Air is pumped into the bottle via a needle valve stuck through a cork from a wine bottle. Eventually the air pressure in the bottle forces the cork out and the bottle shoots into the air at tremendous speed. This is very impressive indeed, but just a bit too dangerous for children to try on their own. Teacher or adult supervision is necessary. If the wine cork is not a tight fit into the bottle, try wrapping some tape around it. It also helps to cut the cork in half if the needle valve is no long enough to go right through. Put some vaseline around the valve to make a good seal with the cork. Let us know how you got on.
Ever wondered how a submarine can sink, only to rise again? Well after this experiment you will hopefully be no longer ignorant. Take a 1.5 litre or 2 litre plastic bottle and fill it to the brim with water. Put in a pen top which has been sealed with blu-tack at the top. The other part of the pen top should still be open. A blu-tack weight should be added to the end of the pen top to make sure that it stays upright in the water. Screw the top on tightly. When you squeeze the bottle hard, the air in the pen top is compressed so that it now contains enough water to make it sink. When you leave it go, the air is no longer compressed and the pen-top has enough buoyancy to rise to the top. In a submarine, tanks are filled with water to make it sink. These are blown out again with compressed air to make it rise. Let us know how you got on.