Monday, 21 December 2009
Wednesday, 16 December 2009
Teacher had a fish that floats in water. He floated in a 2litre bottle.
He had his own air tank (a biro cap, with no hole in the top, held on to the fish with a paper clip and elastic band). We had to figure out a way to get the fish to sink and then float again. We tried turning the bottle upside down (couldn't do this in the sea though), shaking the bottle and holding it sideways. The way to get the fish to sink was to squeeze the bottle. When you do this, the fish sinks to the bottom, and when you stop squeezing, the fish floats again.
This happens because the air in the pen top helps the fish float. When you squeeze the bottle, the air in the cap gets squashed a little (it compresses). This means that the bottle fills a little with water instead. Now the fish hasn't enough air to keep him floating, and the fish sinks.
When you stop squeezing, the air in the pen cap expands again, and now there is enough air in the cap again so the fish can float. We also tried this with a diver and it works in just the same way.
We got a cardboard boat to float on the water. The top of the water has surface tension on it. It is like a skin made by water molecules holding tightly on to one another. The boat floated, but didn't move. When we put just one drop of washing up liquid at the back of the boat, the surface tension is broken and the boat shoots forward. This was really impressive, but we could only do it once. (Actually, we did manage to try again, but only after the basin had been washed and dried to get rid of all traces of wash up liquid). We can't wait to try this in the bath.
Normally when you spill water out of a jug, it will fall straight down. It is gravity that pulls it down. We could get water to spill sideways. First of all we tried lots of things - pouring it out of the side or the back of the jug, using our fingers or hands to get the water to spill sideways. We managed best of all when we used a piece of string, and got the water to run sideways along the string. Water sticks to string with surface tension. Surface tension is like a skin of water caused by water molecules holding tightly on to one another. They were holding so tightly to each other around the string, that even when the string is held sideways, the water will hold on to it and drip sideways, instead of straight down.
We did some interesting science that we can easily practise in the bath at home. We got a bottle and filled it with water, put a hand on top, turned the bottle over and took the hand away. We had to guess what would happen.
It was as we thought - the water that was in the bottle rushed out once the hand was taken away. The second time we tried this, we only took our hand away when the bottle was under water. This time the water stayed in the bottle.
This is because the water in the bottle wanted to get out, while the water in the basin wanted to get in, so the water ended up going nowhere and stayed in the bottle.
Next we got a yoghurt pot and a square of cardboard. We filled the pot with water, put the card on top, turned the pot and card upside down and took our hand away. Surprise, surprise, the card stayed on the bottom of the pot without falling off. This is because the air on the bottom of the card is pushing the card up into the pot, and the water is trying to get out, so both end up going nowhere at all.
After break we had another surprise: Ms. Keenan's class gave a wonderful performance of the nativity. We loved all the great songs and costumes. It really showed us the true message of Christmas.
Tuesday, 15 December 2009
Ms. Crotty and Ms. Ferguson treated us to a wonderful Christmas show. It was all about a star who didn't want to shine more brightly than the others. In the end she turned out to be the star over Bethlehem, and we were all delighted she shone so brightly. The show was fantastic, with catchy songs, and some really fantastic actors and actresses. They had so many lines to say. We are all really proud of them.