We got a nice orange balloon and blew it up to see whether it could be blown up quite big or not. As you can see, we could blow it up to quite a big size.
Next teacher got two bottles. She put the balloon into what looked like an empty 2litre bottle. (Actually, we knew that it was not an empty bottle because there was air already in the bottle.) One of the boys tried to blow up the balloon in the bottle.
It was impossible to blow it. This is because the bottle was already full of air so we couldn't blow up the balloon - no more air would fit in the bottle.
Last of all teacher put the balloon into a 2litre bottle that had the bottom cut off. This time it was really easy to blow up the balloon because when the balloon was inflated, the air in the bottle got pushed out the cut end of the bottle to make room for the air being blown into the balloon. This is an investigation that would be easy to try at home.The (almost) Un-burstable Balloon
Normally if you prick a balloon with a pin the balloon will burst immediately, but we thought of a way to stop the balloon bursting so quickly. We needed a balloon, a pin and some sticky tape. 
We guessed that the teacher should put some sticky tape on to the balloon. Then we stuck the pin into the part of the balloon with sticky tape on it. The balloon did burst eventually, but it took a while to burst, unlike a balloon with no tape on it, which bursts immediately.
This is because usually the rubber in the balloon very quickly pulls away from the place in which the pin is stuck, causing the balloon to explode. With the sticky tape in place, the parts of the balloon next to the hole cannot move. They stay still and the pin acts as a plug in the hole it has made.
Sinking Paper
We needed 2 piles of books and a sheet of paper for this investigation. We put the piece of paper over the gap between the two piles of books. We had to guess what would happen to the paper if we blew hard in the tunnel between the books. Some of us guessed that the extra air in the tunnel would make the paper rise, and others guessed that the paper would fall if we blew the air from out of the tunnel.
One of the boys tried blowing hard........the paper got pushed downwards when he blew the air out of the tunnel. This happens because the air pressure in the tunnel lowers when we speed up the air in the tunnel. The air pressure on top of the sheet of paper then pushes the paper down.Looking at air pressure
We got a plastic bottle, put the cap on and squeezed the bottle. We couldn't squeeze it much because the air inside the bottle wouldn't let us. When we stopped squeezing the bottle went back to its own shape again.
We took off the lid and squeezed the bottle. When we stopped squeezing the bottle went back to its own shape again.
The last time we took the lid off the bottle, squeezed the bottle, put the lid on as we were
squeezing, then stopped squeezing. This time the bottle didn't go back to its own shape again. That is because the air pressure outside the bottle is higher than the air pressure inside the bottle. When we then took the cap off the bottle, the air came rushing back in and the bottle could go back to its proper shape again.
Making a ruler heavier
Teacher balanced a ruler on a chair.
It only took a tiny touch of a baby finger to knock the ruler down. The next time teacher balanced the same ruler on the same chair but she put a small sheet of newspaper on top of the ruler. It was really hard to knock the ruler off the chair with the newspaper on top.
That is because this time the air pressing down on the newspaper puts pressure on the ruler, making it much more difficult to lift.
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