Fair tests and variables · Year 3
A scientific investigation starts with a question, such as “Does the temperature of water change how fast sugar dissolves?” To answer it fairly, you change one thing, measure one thing and keep everything else the same. That is a fair test.
Key facts
- The independent variable is the one thing you change. The dependent variable is what you measure. Control variables are everything you keep the same.
- A fair test changes only one variable, so any difference in the results must be caused by that change.
- A prediction says what you think will happen and why: “The hotter the water, the faster the sugar will dissolve, because the particles move faster.”
- Repeat each measurement and work out a mean. Repeats make results more reliable and show up anomalies (results that don’t fit).
- A categoric variable has names or groups (the type of surface); a continuous variable is a measured number (the temperature, a length).
- Repeatable: you get similar results when you do the test again. Reproducible: someone else gets similar results.
- A control, such as a plant given no plant food, gives you something to compare against.