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Primary Science · Year 6Chapter 1 · Working scientifically (Years 5-6)
Year 6 Science · Working scientifically (Years 5-6) · Lesson 1.2

Year 6 Science: Taking accurate measurements

Part of the Year 6 Science working scientifically (years 5-6) chapter. Chapter overview · whole chapter on one page

1.2

Taking accurate measurements

Year 6
WS2: take measurements with increasing accuracy and precision, taking repeat readings when appropriate
Story. Tom measures the water soaked up by Towel A once, and gets 14 mL. “That is the answer,” he says. Aisha says, “One reading is not enough. Let’s repeat it three times and find the mean.” Their teacher nods. “Repeats show how reliable a result is.”

Accuracy means how close a measurement is to the true value. Precision means how close repeated measurements are to each other.

To improve accuracy, read the scale at eye level, use a suitable instrument, and repeat each measurement. The mean of the repeats is found by adding them together and dividing by how many there are.

A measuring cylinder shows its scale in millilitres. Read the bottom of the curve of the liquid, which is called the meniscus, with your eyes level with the line.

01020304050mLliquid level
A measuring cylinder with the liquid at 34 mL.

Tom and Aisha put the results of three trials into a table. Each mean is the total of the three trials divided by three.

TowelTrial 1 (mL)Trial 2 (mL)Trial 3 (mL)Mean (mL)
Towel A14151314
Towel B9101110
Towel C19182019

Key ideas

  • Repeat a measurement, and find the mean of the repeats.
  • The mean is the total divided by the number of results.
  • Read a measuring cylinder with your eyes level with the liquid.
  • A result that is far from the others may be an outlier, and should be checked.
Worked example 1.2.1
Read the measuring cylinder in section 1.2. The liquid is at 34 mL. Write the reading in millilitres.

Method. Find the level of the liquid on the scale.

  1. Find the scale. The scale on the measuring cylinder counts up in millilitres.
    mL
  2. Read the level. The liquid level sits at the 34 mL mark, with eyes level with the line.
    34
  3. Write the answer.
    34 mL

Check. Every small line on this cylinder is 1 mL. ✓

Watch out. Read the bottom of the curve, not the top edge of the liquid.

Worked example 1.2.2
Towel C was measured three times: 18 mL, 19 mL and 20 mL. What is the mean? Write the answer in millilitres.

Method. Add the three trials, then divide by three.

  1. Add the trials. The total of the three trials is 18 + 19 + 20.
    18 + 19 + 20 = 57
  2. Divide by three. There are three trials, so divide the total by 3.
    57 divided by 3 is 19
  3. Write the answer.
    19 mL

Check. The mean is 19 mL, and the three trials are close together. ✓

Watch out. Divide by the number of trials, which is three here.

Worked example 1.2.3
A pupil measured a stick four times: 42 cm, 43 cm, 61 cm and 42 cm. Which result is an outlier? Write the number.

Method. Look for the result that is far from the others.

  1. Compare the results. Three results are 42 or 43, which are close together.
    close together
  2. Find the one far away. The result 61 is far from the others, so it is an outlier.
    61
  3. Write the answer.
    61

Check. Check the 61 cm reading again, because it may be a mistake. ✓

Watch out

Watch out: a single measurement does not show whether a result is reliable. Repeats show whether the readings are close together.

Exam tip

Exam tip. Always say how many repeats you made, and find the mean of the repeats.

Try it (with your teacher, or a grown-up at home). Measure the length of a pencil three times with a ruler. Read the scale at eye level each time. Write the three results and find the mean. Do you get the same number each time? Which result is an outlier, if any?

Exercise 1B  Taking accurate measurements

1
FLook at the table in section 1.2. How many trials did Tom and Aisha do on each towel? Write the number.
2
FLook at the measuring cylinder in section 1.2. Write the reading in millilitres.
3
FWhat is the mean of 9 mL, 10 mL and 11 mL? Write the answer in millilitres.
4
FWhat is the total of Towel A's three trials, 14 mL, 15 mL and 13 mL? Write the number.
5
FWhich towel has the largest mean in the table in section 1.2? Write the name.
6
FWhy do we repeat a measurement? Write one reason.
7
PSAli measures a stick three times: 17 cm, 18 cm and 19 cm. What is the mean? Write the answer in centimetres.
8
PSLeah says her three results were 20 mL, 21 mL and 30 mL. Which result should she check again, and why? Write the result.
9
PSThe liquid in a measuring cylinder is level with the third small line after the 20 mL mark. Each small line is 1 mL. Write the reading.
10
RTom says his result of 14 mL is accurate because he got 14 mL once. Is Tom right? Write no, and give one reason.
11
RAisha's three results are 9 mL, 10 mL and 11 mL. Tom's are 4 mL, 10 mL and 16 mL. Both have a mean of 10 mL. Who has the more precise results? Write Aisha or Tom.
12
RExplain why the mean of several repeated results is more useful than one result. Write one sentence.

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