Year 3 Science: Careful observations and accurate measurements
Part of the Year 3 Science working scientifically chapter. Chapter overview · whole chapter on one page
Careful observations and accurate measurements
An observation is something we notice with our senses or with a tool. A careful observation looks closely, uses the same method each time, and records exactly what we see.
A measurement is a number with a unit, such as 7 cm, 60 ml or 18 °C. We use standard units: centimetres (cm), millilitres (ml), grams (g), kilograms (kg), seconds, minutes and degrees Celsius (°C).
To measure accurately:
- start a ruler at 0;
- read the scale at eye level, straight across from the mark;
- read to the nearest mark and write the unit;
- repeat the measurement to check it.
A thermometer measures temperature. The liquid inside rises when it gets warmer. A measuring cylinder measures the volume of a liquid in millilitres (ml). A data logger is a small electronic device that records readings, such as temperature, at set times.
Practice only: observing over time means looking at the same thing again and again and writing down what changes. It is practice for careful observation, and it is not a separate statement.
Key ideas
- Use standard units, and write the unit with every measurement.
- Start a ruler at 0 and read it at eye level.
- A thermometer measures temperature in degrees Celsius (°C).
- A data logger records readings at set times, without a person.
Method. Read the scale, then find the mark that the red liquid reaches.
- Find the scale. The numbers go up in steps of 5, with a small mark for each degree.0, 5, 10, 15, 20, 25, 30
- Find the level of the red liquid. The liquid stops above the 15 mark, at the third small mark.above 15
- Count the marks above 15. Three small marks above 15 make 18.15 + 3 = 18
- Write the answer. 18 °C
Check. The thermometer reads 18 degrees, the same as the data logger at 11 am. ✓
Watch out. Read the number on the scale, then add the small marks. Do not guess.
Method. Start at 0, then read the other end of the stick.
- Find the 0 mark. Measuring starts at 0, so the stick begins at 0.starts at 0
- Read the other end. The end of the stick is at the 7 cm mark.ends at 7
- Write the length with the unit. A length is written in centimetres, cm.7 cm
- Write the answer. 7 cm
Check. Count along the ruler from 0 to 7, one centimetre at a time. ✓
Watch out. If you do not start at 0, the answer will be wrong.
Method. Find the scale, then read the level of the water.
- Find the scale. The numbers go up in steps of 20 ml, with a mark every 10 ml.0, 20, 40, 60, 80, 100
- Find the water level. The blue line is at the mark for 60 ml.blue line at 60
- Write the answer with the unit. The volume of a liquid is measured in ml.60 ml
- Write the answer. 60 ml
Check. The blue line sits level with the 60 mark. ✓
Watch out. Read the scale at eye level. Looking from above or below can give a wrong number.
Watch out
Watch out: a measurement with no unit does not say what was measured. “7” could mean 7 cm, 7 ml or 7 °C.
Try it at home or school (with a grown-up). Pour 100 ml of water into a jar, using a measuring jug. Put a strip of tape on the jar to mark the water level. Look at the jar at the same time each day for a few days, and write down the level. (This is practice only: observing over time.)
Exam tip
Grown-up tip. Ask: “What is the unit? Where does the scale start? Can you read it again, at eye level?”
Exercise 1C Careful observations and accurate measurements
Method. Find the 5 mark, then count the small marks above it.
- Find the 5 mark. The number 5 is labelled on the scale.5
- Count the small marks above 5. The liquid stops two small marks above 5.5 + 2 = 7
- Write the answer. 7 °C
Check. Two marks above 5 is 7 degrees. ✓
Method. Start at 0 and read the end of the stick.
- Find the 0 mark. The stick starts at 0.starts at 0
- Read the end. The stick ends at the 9 cm mark.ends at 9 cm
- Write the answer. 9 cm
Check. Count from 0 to 9 along the ruler. ✓
Method. Read the level of the water on the scale.
- Find the scale. The numbers go up in steps of 20 ml.0, 20, 40
- Read the water level. The blue line is at the 40 mark.blue line at 40
- Write the answer. 40 ml
Check. The level is at 40 ml. ✓
Method. Think about what mass is, and which unit measures it.
- Think about mass. Mass is how heavy something is. A pencil case is light.light: grams
- Check the other unit. Kilometres measure distance, not mass.km: distance
- Write the answer. g
Check. Grams are used for small masses. ✓
Method. Think about the tool for temperature.
- Think about the job. We want to know how hot or cold something is.temperature
- Name the tool. A thermometer measures temperature in degrees Celsius.thermometer
- Write the answer. thermometer
Check. A ruler measures length, not temperature. ✓
Method. Compare the two lengths using the same unit.
- Change the units. 1 cm = 10 mm, so 6 cm = 60 mm.6 × 10 = 60
- Compare. The two lengths are equal.60 mm = 60 mm
- Write the answer. the same length
Check. 6 cm is the same as 60 mm. ✓
Method. Change both masses to the same unit.
- Change the units. 1 kg = 1000 g.1000 g
- Compare. 1000 g is more than 900 g.1000 > 900
- Write the answer. 1 kg
Check. 1 kg is heavier than 900 g. ✓
Method. Think about where your eyes should be.
- Think about the reading. The level of the water is seen most clearly straight across.straight across
- Choose the answer. Reading at eye level helps to avoid a wrong reading.eye level
- Write the answer. eye level
Check. Look straight across at the water level. ✓
Method. A standard unit is a unit that everyone agrees on, such as cm.
- Read A. Spoons are not a standard unit.A: spoons
- Read B. Centimetres are a standard unit.B: cm
- Write the answer. B
Check. Centimetres are a unit that everyone agrees on. ✓
Method. Think about what a data logger does.
- Think about the job. A data logger records readings at set times, by itself.by itself
- Decide. So nobody has to write each reading down as it happens.no person needed
- Write the answer. no
Check. The data logger records 17 °C at 10 am on its own. ✓
Method. Think about what we want to see over time.
- Think about the change. We want to see how the level changes from day to day.change each day
- Choose the record. A table with a reading for each day shows the change. One reading does not.table
- Write the answer. a table with a level for each day
Check. Each day gives a new reading to compare. ✓
Method. Think about how each measurement was made.
- Look at Aisha. She read the ruler at a slant, which can give a wrong number.slant
- Look at Ben. He read from 0 at eye level, but the two answers still differ, so both should check again.differ
- Write the answer. Accept any answer that says both should measure again, reading from 0 at eye level, because a slanted reading can give a wrong number.
Check. Repeat the measurement to check the answer. ✓
Method. A careful observation says what we see and how we know.
- Choose what to observe. We observe the leaf.leaf
- Add a tool or unit. A unit or a tool shows how the observation was made.cm or ruler
- Write the answer. Accept any careful observation that uses a tool or a unit, such as “The leaf is 6 cm long, measured with a ruler.”
Check. A tool or a unit makes the observation careful and checkable. ✓