Year 5 Science: Testing a mechanism fairly
Part of the Year 5 Science levers, pulleys and gears chapter. Chapter overview · whole chapter on one page
Testing a mechanism fairly
A fair test on a mechanism changes only one thing, such as the set-up of the pulley. The load is kept the same, the number of trials is repeated, and the results are recorded in a table.
A conclusion must match the evidence. It should say what changed, and what happened, without going beyond the results.
| Set-up | Weights needed to lift the same load |
|---|---|
| no pulley, lifting the load straight up | 8 |
| a fixed pulley, fixed to a support | 8 |
| a movable pulley, which moves with the load | 4 |
Key ideas
- A fair test changes only the set-up of the mechanism, and keeps the load the same.
- Record the results in a table with units, and repeat the test to check them.
- A conclusion must match the evidence in the table.
- Say how much you trust the result, and why.
Method. Compare the movable pulley with no pulley.
- Compare the rows. The movable pulley needed 4 weights, but no pulley needed 8.4 and 8
- Write the conclusion. So the movable pulley made the lift easier, needing about half the weights.easier
- Write the answer. the movable pulley made the lift easier
Check. The conclusion matches the table. ✓
Method. Think about what changed.
- Think about the changes. Changing two things at once means the test is not fair.two things
- Decide. So the test is not fair, and the answer is no.no
- Write the answer. no
Check. A fair test changes only one thing. ✓
Method. Think about repeats.
- Think about the repeats. Repeats that agree make the result more reliable.agree
- Decide. So the result can be trusted more, and the answer is yes.yes
- Write the answer. yes
Check. Repeat trials help us trust a result. ✓
Watch out
Watch out: a conclusion must not go further than the evidence. The table shows fewer weights for a movable pulley, but it does not show what happens to the rope length.
Try it (with your teacher or a grown-up). Repeat the pulley test from section 10.2 with your teacher, changing only the set-up each time. Write a short report with three parts: what you did, what you found, and your conclusion. Say whether your test was fair.
Exam tip
Grown-up tip. Ask: “What did you change? What did you keep the same? Does your conclusion match your results?” Let your child read the report aloud.
Exercise 10E Testing a mechanism fairly
Method. Read section 10.5.
- Read the description. A fair test changes only one thing, such as the set-up of the pulley.set-up
- Name the thing. So the thing changed on purpose is the set-up of the pulley.the set-up of the pulley
- Write the answer. the set-up of the pulley
Check. The load is kept the same. ✓
Method. Read the key ideas in section 10.5.
- Read the key idea. The load is kept the same in a fair test.kept the same
- Choose the word. So the load is kept the same.load
- Write the answer. load
Check. Only the set-up changes, so the load must be kept the same. ✓
| Set-up | Weights needed to lift the same load |
|---|---|
| no pulley, lifting the load straight up | 8 |
| a fixed pulley, fixed to a support | 8 |
| a movable pulley, which moves with the load | 4 |
Method. Read the movable pulley row.
- Read the row. The movable pulley row shows 4 weights.4
- Write the number. So the answer is 4.4
- Write the answer. 4
Check. Check the row name before you answer. ✓
| Set-up | Weights needed to lift the same load |
|---|---|
| no pulley, lifting the load straight up | 8 |
| a fixed pulley, fixed to a support | 8 |
| a movable pulley, which moves with the load | 4 |
Method. Subtract the movable pulley number from the no pulley number.
- Read the numbers. No pulley needs 8 weights, and the movable pulley needs 4.8 and 4
- Subtract. The difference is 8 minus 4, which is 4.8 - 4 = 4
- Write the answer. 4
Check. Check: 4 + 4 = 8. ✓
Method. Think about what changed.
- Think about the changes. Changing two things at once means the test is not fair.two things
- Decide. So the test is not fair.no
- Write the answer. no
Check. Only one thing should change in a fair test. ✓
Method. Think about repeats.
- Think about the repeats. Repeats that agree make a result more reliable.agree
- Decide. So the answer is yes.yes
- Write the answer. yes
Check. Repeat trials help us trust a result. ✓
Method. Think about what the test shows.
- Think about the test. The test only compares a movable pulley with no pulley and a fixed pulley.only compares
- Decide. So the conclusion goes beyond the evidence, and the answer is no.no
- Write the answer. no
Check. A conclusion must not go beyond the evidence. ✓
Method. Think about what makes the test fair.
- Think about the test. Only the effort arm should change in a lever test.effort arm
- Write one thing. The load, the pivot and the weights must stay the same.stay the same
- Write the answer. Accept any one of: the load, the pivot position, the same weights.
Check. Keeping one thing the same makes the test fair. ✓
Method. Think about repeats.
- Think about one trial. One trial can be affected by a mistake or by chance.mistake
- Write the reason. Repeats show whether the results agree, which makes the result more trusted.agree
- Write the answer. Accept any sentence that says repeats show whether the results agree, so a single mistake is less likely to affect the result.
Check. Agreement between trials increases trust. ✓
Method. Think about the evidence.
- Think about the table. The table shows only the results of the test.only the results
- Write the reason. So a conclusion must not claim more than the evidence shows.not claim more
- Write the answer. Accept any sentence that says a conclusion must match the evidence, and must not claim more than the table shows.
Check. A conclusion should match its evidence. ✓