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When we need to choose a material for a particular job, we do experiments to find out which material will have the best properties.

It is important to make our experiments fair. This usually means keeping things the same when you are comparing the different materials, so it is a fair comparison.

To find out which material would be best for insulating a hot water tank (keeping it warm), we could do this experiment.

1. Take four empty aluminium drinks cans.
2. Wrap a possible insulating material around each can, e.g. sheets of newspaper, a sheet of cotton wool, some fleece fabric, some aluminium foil.
3. Ask an adult to pour some hot tap water carefully into each of the cans. Take the temperature of the water in each can using a thermometer. Write this into a results table.
4. After 10 minutes, take the temperature again in each can and write it down.
5. Work out which can has cooled the least. This can has the best insulation.

Your results table might look like this:

Think about what you need to keep the same in this experiment. What else might affect how much the water cools down? This experiment will only be a comparative test if you keep these things the same for all four cans:

• same size can
• same amount of water in each can
• same starting temperature of the water
• same length of time
• same thickness of insulating material

Keeping the thickness the same in this kind of experiment is very hard to do! You would probably need to wrap 50 or more turns of foil or paper around the can to make the insulation the same thickness as the cotton wool or fleece. Sometimes it is very hard (or impossible) to make an experiment a totally fair test.

Investigate which material would be best for making a waterproof jacket

Think about which materials you could use such as:

• cling film
• paper towel
• cotton
• fleece
• kitchen foil

Before you start your investigation, make a prediction:I predict that ____________ will be best for making a waterproof jacket because ___________.

How are you going to carry out your investigation?

• You could use a bowl, some large elastic bands to secure the different materials you are testing over the top of the bowl, and a jug with some water in.

Remember to:

• make it as fair a test as possible
• record your results clearly
• write a conclusion