Every investigation has three kinds of variables. The one you change on purpose is the independent variable. The one you measure is the dependent variable: it depends on what you changed. Everything else you keep the same; these are the control variables, and they make the test fair.
Planning starts with a question, such as 'Does the temperature of water change how fast sugar dissolves?' Here you change the water temperature, measure the time to dissolve, and keep the amount of water, the size of the sugar cube and the stirring the same.
Worked example
Pupils test how the length of a string affects a pendulum's swing time. What do they change, measure and keep the same?
- Change: the length of string.
- Measure: the time for ten swings.
Answer:Keep the same: the mass on the end and the starting angle.
Key words
- independent variable
- what you change
- dependent variable
- what you measure
- control variable
- what you keep the same
- investigation
- a planned test to answer a question
New questions every time.