Year 5 Science: Measuring with increasing accuracy
Part of the Year 5 Science working scientifically: planning and reporting chapter. Chapter overview · whole chapter on one page
Measuring with increasing accuracy
Precision means how finely a measurement can be read. A ruler marked in millimetres is more precise than a ruler marked in centimetres, because its smallest step is smaller.
Accuracy means how close a measurement is to the true value.
To improve a measurement, use an instrument with a finer scale, and take repeat readings. Add the readings together and divide by how many there are. This is the mean. If one result is very different from the others, it is anomalous. Check it, and if there is a clear reason it was wrong, leave it out of the mean.
| Instrument | Smallest step on the scale |
|---|---|
| Ruler marked in cm | 1 cm |
| Ruler marked in mm | 1 mm |
| Measuring cylinder marked every 10 ml | 10 ml |
| Measuring cylinder marked every 1 ml | 1 ml |
Key ideas
- Precision is how finely a measurement can be read.
- Accuracy is how close a measurement is to the true value.
- Repeat readings are added together and divided by the number of readings to find the mean.
- An anomalous result is very different from the others, and can be left out of the mean if there is a clear reason.
Method. Add the three trials, then divide by three.
- Add the trials. The three trials add together to make 129 cm.41 + 45 + 43 = 129
- Divide by the number of trials. There are three trials, so divide 129 by 3.129 divided by 3 is 43
- Write the answer. 43
Check. Check: 43 + 43 + 43 = 129. ✓
Watch out. Divide by the number of readings, which is three here.
Method. Compare the smallest steps.
- Read the two rulers. One ruler has steps of 1 cm, and the other has steps of 1 mm.1 cm and 1 mm
- Choose the finer scale. A smaller step means the ruler can be read more precisely.smaller step
- Write the answer. mm
Check. There are 10 millimetres in every centimetre. ✓
Method. Take out the anomalous result, then find the mean of the rest.
- Leave out the anomaly. The 73 cm result is very different from the others, so it is left out. The other three are 44, 46 and 45.44, 46, 45
- Find the mean. The three add to 135 cm, and 135 divided by 3 is 45.135 divided by 3 is 45
- Write the answer. 45
Check. Check: 45 + 45 + 45 = 135. ✓
Watch out. Divide by 3, not 4, because the anomalous result has been left out.
Watch out
Watch out: a repeat reading is not the same as a copy. Measure again each time, and then find the mean. If you leave out a result, divide by the number of results that are left.
Try it (with your teacher or a grown-up). Measure the same book three times with a ruler, and write each length down. Then find the mean. Did you get the same answer each time? Measure once more with a ruler that has a finer scale, if you have one, and compare the two.
Exam tip
Grown-up tip. Ask: “Which measurement did you trust most, and why?” Let your child add the readings and divide by the number of readings.
Exercise 1B Measuring with increasing accuracy
Method. Look at the smallest step on each scale.
- Compare the steps. A ruler marked in millimetres has smaller steps than a ruler marked in centimetres.smaller steps
- Write the unit. The smallest step is 1 mm.mm
- Write the answer. mm
Check. There are 10 mm in 1 cm, so mm gives a finer reading. ✓
Method. Find the cylinder with the smaller step.
- Read the table. One cylinder is marked every 10 ml, and the other is marked every 1 ml.10 ml and 1 ml
- Choose the finer scale. The smaller step, 1 ml, is the more precise cylinder.1 ml
- Write the answer. 1 ml
Check. A step of 1 ml is ten times finer than a step of 10 ml. ✓
Method. Add the trials and divide by three.
- Add the trials. The trials add to 129 cm.41 + 45 + 43 = 129
- Divide by three. Divide 129 by 3 to find the mean.129 divided by 3 is 43
- Write the answer. 43
Check. Check: 43 + 43 + 43 = 129. ✓
Method. Add the three results, then divide by three.
- Add them. The three results add to 243 mm.80 + 82 + 81 = 243
- Divide. Divide 243 by 3 to get the mean.243 divided by 3 is 81
- Write the answer. 81
Check. Check: 81 + 81 + 81 = 243. ✓
Method. Add the three numbers, then divide by three.
- Add them. The three numbers add to 36.10 + 12 + 14 = 36
- Divide. Divide 36 by 3 to find the mean.36 divided by 3 is 12
- Write the answer. 12
Check. The mean of 10, 12 and 14 is in the middle, which is 12. ✓
Method. Find the result that is very different from the others.
- Look at the readings. Three readings are close to 45 cm, but 73 cm is much bigger.much bigger
- Name the anomaly. So the anomalous result is 73 cm.73
- Write the answer. 73
Check. Check the anomaly before leaving it out. ✓
Method. Leave out the anomaly, then find the mean of the rest.
- Leave out the anomaly. Without 73 cm, the readings are 44, 46 and 45.44, 46, 45
- Find the mean. They add to 135, and 135 divided by 3 is 45.135 divided by 3 is 45
- Write the answer. 45
Check. Check: 45 + 45 + 45 = 135. ✓
Method. Find the result that is very different from the others.
- Compare the heights. Three of the heights are close to 30 cm, but 52 cm is far bigger.far bigger
- Name the anomaly. So the anomalous result is 52 cm.52
- Write the answer. 52
Check. Priya should check this result before she leaves it out. ✓
Method. Read the two definitions in section 1.2.
- Read the definitions. Accuracy is how close a measurement is to the true value.close to the true value
- Choose the word. So the word is accurate.accurate
- Write the answer. accurate
Check. Precise means how finely a result can be read. ✓
Method. Think about what repeat readings are used for.
- Think about repeats. Repeat readings are added together and divided by how many there are.added and divided
- Fill the gap. The number found this way is the mean.mean
- Write the answer. mean
Check. Repeats also show whether the readings agree with each other. ✓
Method. Think about what a single reading can miss.
- Think about one reading. One reading can be affected by one mistake or by chance.one mistake
- Write the reason. Several readings make a single mistake less important.less important
- Write the answer. Accept any sentence that says repeat readings reduce the effect of one mistake or chance, so the result can be trusted more.
Check. Repeat readings make the result more reliable. ✓