Observing and measuring

Scientists find out about the world by observing carefully with their senses and by measuring. Measuring turns what we see into numbers we can compare, using the right instrument and the right unit.

Key facts

  • We observe with our senses: sight, hearing, smell and touch. Never taste anything in science unless a teacher says it is safe.
  • Length: a ruler or tape measure (mm, cm, m). Mass: a weighing scale (g, kg). Time: a stopwatch (s, min). Temperature: a thermometer (°C). Volume of a liquid: a measuring jug or cylinder (ml, l). Force: a forcemeter (N).
  • Choose an instrument that suits the size of what you measure: a ruler for a pencil, a tape measure or trundle wheel for a playground.
  • Before reading a scale, work out what each small mark is worth. Read it with your eye level with the mark.
  • 1 cm = 10 mm, 1 m = 100 cm, 1 kg = 1000 g, 1 l = 1000 ml and 1 minute = 60 s.
  • Write down what you find straight away, in a table, with the units in the headings.

Worked examples

Example 1

How long is the orange strip?

  1. The strip does not start at 0. It starts at 2 cm.
  2. It ends halfway between 9 and 10: 9.5 cm.
  3. Take the start from the end. 9.5 − 2 = 7.5 cm

Answer: 7.5 cm

Example 2

What temperature does the thermometer show?

  1. The numbers go up in tens, and there are 5 spaces between 30 and 40, so each mark is 2°C. 10 ÷ 5 = 2
  2. The red liquid is two marks above 30. 30 + 2 + 2 = 34

Answer: 34°C

Example 3

How much water is in the measuring cylinder?

  1. The numbers go up in twenties, with 4 spaces between them, so each mark is 5 ml. 20 ÷ 4 = 5
  2. Read with your eye level with the water. The water is one mark above 60. 60 + 5 = 65 ml

Answer: 65 ml

Example 4

Which instrument and unit would you use to measure the mass of an apple, the time for an ice cube to melt and the length of the school hall?

  1. Mass is measured with a weighing scale; an apple is light, so use grams (g).
  2. Time is measured with a stopwatch; melting takes a while, so use seconds (s) or minutes.
  3. A hall is long, so use a tape measure (or trundle wheel) in metres (m).

Answer: a weighing scale in grams; a stopwatch in seconds or minutes; a tape measure in metres