Year 4 Science: Setting up a fair test
Part of the Year 4 Science working scientifically revisited chapter. Chapter overview · whole chapter on one page
Setting up a fair test
A fair test is a test where only one thing is changed. The thing we change is the variable we choose to change. The thing we measure is the result. Everything else must be kept the same, so that the test is fair.
We also repeat each test. Repeating the test (called a trial) helps us check that a result is not a one-off. We then find an average, which is the total divided by the number of trials.
This table shows how the three towels were tested. Each towel was dipped in the same 50 ml of water for 10 seconds, three times.
| Towel | Trial 1 (ml) | Trial 2 (ml) | Trial 3 (ml) | Average (ml) |
|---|---|---|---|---|
| Towel A | 9 | 11 | 10 | 10 |
| Towel B | 16 | 15 | 17 | 16 |
| Towel C | 12 | 14 | 13 | 13 |
Key ideas
- A fair test changes only one thing.
- The thing measured is the result, and everything else is kept the same.
- Repeat each test three times, and find the average.
- If two things change, the test is not fair.
Method. Find the thing that changes.
- Read the sentence. Ruby changes the brand of towel.brand of towel
- Name the part. The thing that is changed is the variable, so the variable is the brand.brand
- Write the answer. brand
Check. The water and the time are kept the same. ✓
Watch out. Measured and changed are different parts of a test.
Method. Count the things that change.
- Count the changes. Aisha changes two things: the towel and the amount of water.two things
- Decide. A fair test changes only one thing, so this test is not fair.not fair
- Write the answer. no
Check. A fair test changes only one thing. ✓
Method. Read the sentence about the trials.
- Read the sentence. Ruby does three trials for each towel.three trials
- Write the number. So she does three trials for one towel.three
- Write the answer. 3
Check. Three trials for each towel, with the average found from them. ✓
Watch out
Watch out: a test is only fair if you keep everything else the same. Changing the water, the time and the towel at once tells you nothing about any one of them.
Try it at home or school (with a grown-up). Choose a plastic lid and a sheet of paper towel. Put 20 ml of water on each one, using a spoon, with a grown-up. Change only the surface, and keep the water and the time the same. Write down what you kept the same.
Exam tip
Grown-up tip. Ask: “What did you change? What did you keep the same?” Let your child name the variable, the result and one thing that was kept the same.
Exercise 1B Setting up a fair test
Method. Read the definition of a fair test.
- Read the definition. A fair test is a test where only one thing is changed.only one thing
- Write the answer. 1
Check. Changing one thing means we know what caused the result. ✓
Method. Count the things that change.
- Count the changes. Ruby changes two things: the towel and the water.two things
- Decide. A fair test changes only one thing, so the answer is no.no
- Write the answer. no
Check. Two changes make the result impossible to explain. ✓
Method. Read the key idea in section 1.2.
- Read the key idea. Everything else must be kept the same, so the test is fair.kept the same
- Write the answer. same
Check. Same means it does not change between trials. ✓
Method. Read the table in section 1.2.
- Read the first column. The result is the thing we measure, which is the millilitres of water soaked up.measured
- Check the words. Measured is the word for the result.measured
- Write the answer. measured
Check. Changed is the one thing we choose to change. ✓
Method. Think about what stays the same in every trial.
- Think about the test. Each towel uses the same amount of water and the same time.same amount of water
- Write one thing. For example, the amount of water must stay the same.amount of water
- Write the answer. Accept any one of: the amount of water, the time, the size of the towel.
Check. Keeping one thing the same makes the test fair. ✓
Method. Look at what changes.
- Look at the cubes. Mo changes the size of the cube, which is a thing he should keep the same.size
- Decide. Because the size changes between tests, the test is not fair. The answer is no.no
- Write the answer. no
Check. The size of the cube must be kept the same. ✓
Method. Look at the table.
- Read the columns. The table has columns for trial 1, trial 2 and trial 3.trial 1, 2 and 3
- Count them. There are three trials.3
- Write the answer. 3
Check. Three trials help us find a reliable average. ✓
Method. Think about the test Ali did.
- Read his test. Ali changed two things, so we cannot tell which one caused the result.two things
- Decide. His conclusion is not sound because the test was not fair.not sound
- Write the answer. no
Check. Only one thing should change in a fair test. ✓
Method. Look at the timers.
- Look at the timers. Each towel had its own timer, so the time was not the same for each.not the same
- Write the problem. The time was not kept the same, so the test is not fair.time
- Write the answer. Accept any answer that says the time was not kept the same, because each towel used a different timer.
Check. Using the same timer for every test keeps the time the same. ✓
Method. Think about one thing you could change.
- Think of one thing. The amount of water, or the place, could be changed.one thing
- Write it down. Only one thing should be changed in a fair test.only one
- Write the answer. Accept any one thing, such as the amount of water in the puddle, or the place where it is.
Check. Changing only that one thing keeps the test fair. ✓
Method. Think about one result.
- Think about one trial. One result can be unusual, by chance.unusual
- Write the reason. Repeating the test shows whether the result happens again, and the average is more reliable.more reliable
- Write the answer. Accept any sentence that says repeating shows whether a result is typical, and makes the average more reliable.
Check. Three trials give a better answer than one. ✓