We get different sorts of weather because of the way warm air and cold air move around us in the atmosphere.
What you will need:
- A large, clear tank (an empty fish tank would be ideal)
- Warm and cold water
- Two plastic cups
- Small stones (pebbles)
- Food colouring
What to do:
- Fill the tank with normal water and leave this for a few hours to come to room temperature.
- Place a few small pebbles in each of the two cups to act as weights.
- Pour some hot water and a few drops of red food colouring in one of the cups.
- Fill the other cup with very cold water and add some blue food colouring.
- Place the two cups into the water at the same time, one at either end of the tank - the pebbles should hold the cups at the bottom.
- Carefully watch how the two different coloured waters move. You should see that the warmer red water should rise to the top, and the cooler blue water should sink to the bottom.
Warm air (shown by your warm red water) is less dense than cold air (cold blue water), so warm air rises and pushes down with less pressure than cold air. As air cools, it becomes denser, so it sinks and also pushes down with greater pressure.