Year 3 Science: A fair test with two magnets
Part of the Year 3 Science magnets chapter. Chapter overview · whole chapter on one page
A fair test with two magnets
To compare two magnets, do a fair test. Change only one thing: the magnet. Keep everything else the same:
- the same paper clips, and the same number of clips in the tray;
- the same tray;
- the same end of each magnet, dipped in the same way;
- the same way of lifting the magnet out.
Count the paper clips that stick after each trial. Repeat each test three times. Add the three trials together, then divide by three, to find the average.
Aisha and Sam recorded their results in the table.
| Trial | Magnet A (paper clips) | Magnet B (paper clips) |
|---|---|---|
| Trial 1 | 6 | 9 |
| Trial 2 | 4 | 8 |
| Trial 3 | 5 | 10 |
| Average | 5 | 9 |
Key ideas
- In a fair test of two magnets, change only the magnet.
- Keep the paper clips, the tray and the way of lifting the same.
- Repeat each trial three times, and find the average.
- The magnet with the higher average picked up more paper clips in this test.
Method. Compare the two averages.
- Read the averages. Magnet A averages 5 clips, and Magnet B averages 9 clips.5 and 9
- Choose the bigger one. Nine is more than five, so Magnet B picked up more.Magnet B
- Write the answer. B
Check. Magnet B picked up more clips on average. ✓
Method. Add the three trials, then divide by three.
- Add the trials. The three trials for Magnet A are 6, 4 and 5 clips.6 + 4 + 5 = 15
- Divide by three. Divide 15 by 3 to get the average.15 divided by 3 is 5
- Write the answer. 5
Check. Check: 5 + 5 + 5 = 15. ✓
Watch out. Divide by three, because there are three trials.
Method. Subtract the smaller average from the bigger one.
- Read the two averages. Magnet B averages 9, and Magnet A averages 5.9 and 5
- Subtract. The difference is 9 minus 5, which is 4.9 - 5 = 4
- Write the answer. 4
Check. Check: 5 + 4 = 9. ✓
Watch out. Subtract the smaller average from the bigger one.
Watch out
Watch out: if you use more clips for one magnet, or lift one magnet from a different end, the test is not fair. You will not know which change made the difference.
Try it at home or school (with a grown-up). With a grown-up, put ten paper clips in a tray. Dip one bar magnet into the tray, at the same end each time, and count the clips that stick when you lift it out. Put the clips back in the tray, and repeat three times. Then do the same with a second magnet, using the same ten clips. Find the average for each magnet. Keep magnets away from your mouth.
Exam tip
Grown-up tip. Ask: “What did you keep the same? Which magnet picked up more clips on average?” Let your child add the three trials and divide by three.
Exercise 10F A fair test with two magnets
Method. Find trial 2 in the table.
- Find the row. Trial 2 is the second row of the table.trial 2
- Read the Magnet A column. Magnet A picked up 4 clips in trial 2.4
- Write the answer. 4
Check. Trial 2 is the second row. ✓
Method. Find trial 3 in the table.
- Find the row. Trial 3 is the third row of the table.trial 3
- Read the Magnet B column. Magnet B picked up 10 clips in trial 3.10
- Write the answer. 10
Check. Trial 3 is the third row. ✓
Method. Add the three trials for Magnet B.
- Read the trials. Magnet B picked up 9, 8 and 10 clips.9, 8 and 10
- Add them. Nine, eight and ten make twenty-seven.9 + 8 + 10 = 27
- Write the answer. 27
Check. Divide 27 by 3 to get the average of 9. ✓
Method. Add the three trials for Magnet A.
- Read the trials. Magnet A picked up 6, 4 and 5 clips.6, 4 and 5
- Add them. Six, four and five make fifteen.6 + 4 + 5 = 15
- Write the answer. 15
Check. Divide 15 by 3 to get the average of 5. ✓
Method. Find the average row.
- Read the average row. The average row says 9 for Magnet B.9
- Check the trials. 27 divided by 3 is 9, so the average is correct.27 / 3 = 9
- Write the answer. 9
Check. The average of 9, 8 and 10 is 9. ✓
Method. Compare the three trials for Magnet A.
- Read the trials. Magnet A picked up 6 clips in trial 1, 4 in trial 2 and 5 in trial 3.6, 4, 5
- Choose the most. Six is the most, and it was in trial 1.trial 1
- Write the answer. 1
Check. Six is more than 5 and 4. ✓
Method. Compare the two averages.
- Read the averages. Magnet B averages 9 clips, and Magnet A averages 5 clips.9 and 5
- Decide. Nine is more than five, so Sam is right.yes
- Write the answer. yes
Check. The fair test shows Magnet B picked up more. ✓
Method. Think about what makes a test fair.
- Think about the test. Only the magnet should change, so the other things must stay the same.stay the same
- Write one thing. For example, use the same paper clips each time.same paper clips
- Write the answer. Accept any one of: the same paper clips; the same tray; the same end of each magnet; the same way of lifting.
Check. Keep everything else the same. ✓
Method. Think about what has to stay the same.
- Compare the clips. Magnet A had 20 clips, and Magnet B had 10 clips, so the number of clips is not the same.20 and 10
- Decide. The number of clips must be the same, so the test is not fair.no
- Write the answer. no
Check. Only the magnet should change. ✓
Method. Add the three trials, then divide by three.
- Add the trials. Seven, five and six add up to eighteen.7 + 5 + 6 = 18
- Divide by three. Divide 18 by 3 to get the average.18 divided by 3 is 6
- Write the answer. 6
Check. Check: 6 + 6 + 6 = 18. ✓
Method. Find the average for Magnet D.
- Add the trials. Three, four and two add up to nine.3 + 4 + 2 = 9
- Divide by three. Nine divided by three is 3, so the average is 3 clips.9 divided by 3 is 3
- Compare with Magnet B. Magnet B averages 9 clips, which is more than 3, so Magnet D picked up fewer.fewer
- Write the answer. fewer
Check. Three clips is fewer than nine clips. ✓
Method. Think about one trial.
- Think about a single trial. One trial might be unusual, for example if one clip slips.one unusual trial
- Think about the average. Three trials give a more reliable average than one trial.more reliable
- Write the answer. Accept any sentence that says repeating the test makes the results more reliable, so one unusual trial does not decide the answer.
Check. Repeating the test helps us to be more sure of our results. ✓