Primary Science — Fair Test & Variables Practice
Rule first: three variables, and only one may change
| Variable | What it means |
|---|---|
| Change | The ONE thing you deliberately change (the thing you are testing). |
| Keep the same | Everything else that could affect the result — amount, size, type, time, temperature. |
| Measure | The result you record, with its unit. |
Example. “Which paper towel absorbs the most water?” — change: the brand of towel; keep the same: the size of the sheet, the amount of water (20 ml), the time soaked (1 minute); measure: the mass of water absorbed, in g (or the volume, in ml).
1. Seeds in the light and in the dark
A pupil wants to find out whether light is needed for a seed to germinate. She puts 5 green bean seeds on damp cotton wool in a dish on the windowsill, and 5 more on damp cotton wool in a dish in a dark cupboard. Both dishes are kept at room temperature, and both lots of cotton wool are kept damp with the same amount of water.
(a) What is changed? (b) What is kept the same? (c) What is measured? [3]
(d) Predict what happens in each dish, and explain your prediction. [2]
(e) She finds that both lots of seeds germinate. What does this tell her about whether light is needed for germination? [1]
2. Spot the unfair test
Two pupils want to find out which brand of paper towel absorbs more water.
- Ali puts 1 sheet of Brand A into 20 ml of water for 1 minute.
- Ben puts 2 sheets of Brand B into 20 ml of water for 1 minute.
(a) Give two reasons why this is not a fair test. [2]
(b) Rewrite Ben’s test so that it is fair. [2]
3. Completing a results table
A pupil stirs one spoon of sugar into water at two different temperatures and records the time taken for all the sugar to dissolve. Complete the table, then write a conclusion.
| Temperature of the water (°C) | Time taken to dissolve (s) |
|---|---|
| 20 | 95 |
| 40 | 60 |
| 60 | ________ |
| 80 | ________ |
(a) The pattern is that the time halves each time the temperature rises by 20 °C. Use the pattern to fill in the last two rows. [2]
(b) Write a conclusion for this experiment. Use the words “because” and “faster”. " [2]
(c) Name one thing the pupil must keep the same in this test. [1]
4. Design your own fair test
Your teacher gives you four cups, four materials to wrap around them (wool, aluminium foil, cotton, paper) and a thermometer. Design a fair test to find out which material keeps hot water warm the longest.
(a) What will you change? [1]
(b) What must you keep the same? Give three things. [3]
(c) What will you measure, and at what times? [2]
(d) Write one sentence saying what you think you will find out. [1]