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A variable is a part of a science experiment which can change. In all science experiments variables can be:

• changed
• measured, or
• controlled.

It is really important that only one variable is changed and one measured. All others must all be kept the same. Scientists call these controlled variables.

When all other variables are controlled an experiment is a fair test. You can learn more about .

When planning an investigation, you need to think of the scientific question you are looking to answer.

You then need to decide how you are going to answer that question. Are you going to:

• make observations over time
• look for patterns and relationships
• carry out a fair test

You will also need to think about:

• What your method will be?
• What equipment do you need?

Test your knowledge of planning experiments and variables with the activities below.

Ask a responsible adult to help you with this activity.

You will need sugar or salt to dissolve, and water at different temperatures.

It is very important that you only use hot water if the adult is working with you, because spilling it might hurt you.

1. Put water into three glasses or cups:

   • cold (from the fridge or left outside overnight)
   • medium (half-filled from above and the other half from below)
   • warm (left on the radiator or in the sun)

2. Put one teaspoon of sugar or salt into each cup and stir it until it disappears.

3. Record the time this takes.