Hot air rises

Teacher asked us what we thought would happen if we hung some snake spirals up. Would they stay still? Would they move? We decided to investigate. First we coloured in our snake spirals and then we cut them out. We hung them above various places in the classroom (such as above our desks) but they didn't move at all. Then we hung them above the radiators in our classroom. All of a sudden there was great excitement as our snake spirals began to move. What was different this time that made our snakes move we wondered?? Then we noticed that there was warm air coming from the radiators and it was this warm air rising from the radiators that made the snakes move. Warm air is lighter than cold air. Warm air therefore rises and cold air comes in to take its place. This causes air currants - both indoor and outdoor.

A few days later teacher asked us if anyone could blow up a balloon without blowing in to it. Some people suggested blowing the balloon up with a pump but teacher said that she didn't have a pump so could we think of any other ways. Teacher only had a bowl of very hot water, an 'empty ' plastic bottle and a balloon. Then teacher gave us a clue and asked us to think about what happens to warm air and to think about what keeps a hot air balloon up in the air? We all said that it was the 'fire' ie heat. But how were we going to get hot air into our balloon to make it rise? We knew that we had to place something into the hot water so we placed the 'empty' bottle into the water. Next we placed the balloon on the top of the bottle (where the lid should be) and after a minute or so our balloon was blown up a little. The hot water warmed the air inside the bottle and the warm air rose to blow up our balloon!! The same principle works for hot air balloons and when the heat of the burner inside the balloon is turned up the hot air balloon rises and when the heat of the burner is turned down it goes down. This experiment was great fun.