Earth & Space - Changing materials - Water - P4G10 - ES-C3.4

1. Depending on your class you may feel it appropriate to introduce the terms evaporation and condensation at this point.

2. The children will probably be familiar with making ice-cubes from water and will be aware that when snow melts it turns to water. They will query where the water from the puddles goes to since they cannot see the water vapour in the air.

The air around us is full of water molecules - think how much water appears on the windows as condensation on a cold morning - energetic water molecules hitting the cold surface give up their energy and return to the liquid form. The same happens when a drinks can is taken out of a very cold fridge - water molecules in the air suddenly hit the cold surface, lose their energy and become water.

Evaporation

In a solid the molecules are bound together tightly and don’t need much energy. In a liquid they are bound together quite loosely and move about a lot so need more energy. In a gas the molecules fly about freely and need a lot of energy. - Think of children sitting in a classroom - when they are sitting watching the blackboard they don’t need much energy - like a solid.

When they move about the classroom doing various tasks they need more energy - like a liquid. When they go about to play and run about all over the place they need lots of energy - like a gas!

The children get their energy from eating food- perhaps a play piece!

The molecules in a liquid have to get the energy they need from whatever they are touching - in this case your skin. The energy they take is heat energy - they take heat from your skin and they convert it to the type of energy they need for movement - for them to become a gas.

Remember - energy is never lost but can be changed from one type to another.

4. Demonstrate the Water Cycle using a kettle and a cold jar. Set up a water cycle using a little water sealed in a plastic bag, placed on a sunny windowsill. Observe the changes which take place.

5. Allow the children to suggest their own ideas for keeping a snowball (or ice-cube) solid and try to provide the groups with the materials they suggest.

Wrap up and stay cold!

It is quite a difficult idea for many children to understand that insulating cold things will keep them cold. The idea of wrapping up snow seems quite strange.

You can approach this by talking about ‘wrapping up warm’. What happens when you put a thick coat on? You get warm! What makes you warm? Most children will answer that the coat makes you warm but if you put the coat on a chair, will the chair get warm? No. The coat does not make you warm but stops the heat from your body getting out. In the same way, putting a ‘coat’ on some ice will stop the heat getting in!