In this unit we explore the size of a centimetre and measure objects using the centimetre rulers that we have constructed.
- Recognise the need for a standard unit of length.
- Recognise a centimetre length.
- Estimate and measure to the nearest centimetre.
When students can measure lengths effectively using non-standard units, they are ready to move to the use of standard units. The motivation for moving to this stage, often follows from experiences where the students have used different non-standard units for the same length. They can then appreciate that consistency in the units used would allow for the easier and more accurate communication of length measures.
Students' measurement experiences must enable them to:
- develop an understanding of the size of the standard unit
- estimate and measure using the unit
The usual sequence used in primary school is to introduce the centimetre first, then the metre, followed later by the kilometre and the millimetre.
The centimetre is often introduced first because it is small enough to measure common objects. The size of the centimetre unit can be established by constructing it, for example by cutting 1-centimetre pieces of paper or straws. Most primary classrooms also have a supply of 1-cm cubes that can be used to measure objects. An appreciation of the size of the unit can be built up through lots of experience in measuring everyday objects. The students should be encouraged to develop their own reference for a centimetre, for example, a fingertip.
As the students become familiar with the size of the centimetre they should be given many opportunities to estimate before measuring. After using centimetre units to measure objects the students can be introduced to the centimetre ruler. It is a good idea to let the students develop their own ruler to begin with. For example, some classrooms have linked cubes which can be joined to form 10 cm rulers. Alternatively pieces of drinking straw could be threaded together.
The correct use of a ruler to measure objects requires specific instruction. The correct alignment of the zero on the ruler with one end of the object needs to be clarified.
Metres and millimetres are established using a similar sequence of experiences: first construct the unit and then use it to measure appropriate objects.
- Paper of two different colours
- 1cm grid paper
- Labels from students' clothing
- 1cm cubes
- Metre rulers
- Tape measures
- Streamer or crepe paper
- Begin the session by asking the students to make an outline of their hand on paper and to cut it out and paste it on to a sheet of paper of another colour. Ask them to estimate how many 1 cm blocks wide they think their handspan is and then to measure it. Provide further questions for them to investigate:
Which finger is the longest?
How long is you thumb?
Is your palm longer than your longest finger?
While students are working check that they are using a baseline to start their measuring from and that the blocks are touching.
Who has the largest handspan?
What is the difference between the largest and smallest handspan?
- Ask the students if they know of any other way of measuring in centimetres besides using the blocks. Check their suggestions by placing 1cm blocks on the different measures e.g. 30cm ruler, metre ruler, tape measure.
Explain to the students that they are going to make their own centimetre rulers.
Provide them with 1cm grid paper to cut a strip from and some cardboard to paste it on to.
To complete the task have them number off the lines. Ensure students label the 0 point at one end of the ruler and then put the numbers on the lines, not the spaces.
- Focus on the length of a single cm by asking the students to draw a line that is 1 cm long. Ask them to find objects that are one cm long (or wide). For example, the width of a finger tip can used to estimate a cm.
- Have the students remove their shoe and trace an outline of their foot and then estimate its length in centimetres. They can then measure it accurately with the rulers they have made and record the measurement it. The footprints can be ordered from largest to smallest. The students can also record what place they were in that order e.g. 1st, 14th. 23rd,
- Tell the students they are going to measure different parts of their body and record it under the heading of All About Me. Prior to starting, build a chart of ideas for measuring e.g. smiles, hair, arms (wrists to elbows), legs (knees to ankles), necks, wrists, waists etc.
Pose the problem of how to measure around something. Accept suggestions and provide string and tape measures. Encourage the students to estimate first and to see if there are any patterns and relationships. Is there another part of your body the same as the measurement from wrist to elbow, or around your ankle etc?
- Explain to the students that the PTA has decided to purchase new sports tops for the school and they need information about sizes.
Could we measure one person in the class and have all the tops made using their measurements?
Discuss with the class the range in measurements
Suggest to the students that we could help the PTA by sending them patterns that would fit people in our class.
Show them a sweatshirt and discuss all the measurements that need to be made and provide them with a large sheet of paper to draw their patterns on.
Provide a range of measuring equipment and go over how to use calibrated measures to ensure they are measuring from the first mark or zero and not the edge.
The students could place the school logo on their pattern and then provide measurements for where it is located. Share their finished patterns and discuss the differences.
What was the longest/shortest arm length?
What is the difference between them etc?
- Look at labels from students’ clothing. Highlight the information that is on them.
Size 8, Height 130cm, Chest 68cm, Waist 60cm.
Ask the students if they would expect all 8 year olds to be 130cm. (link back to findings in the previous activity)
Would we expect them to be close to 130cm?
Give the students the opportunity to investigate the heights of eight-year-olds and nine-year-olds. (Relate the investigation to the age of the students in the class)
Discuss methods of measuring longer lengths.
Look at a metre ruler and identify the number of centimetres and show how a 1cm cube fits into the spaces.
Discuss how to measure lengths longer than a metre and have a student demonstrate marking off and repositioning the ruler.
After the students have measured their height ask them to record it on a piece of card and then cut a piece of paper that length. (streamer, crepe papers). Attach this to the edge of the card with tape.
Display the students’ paper heights in order along the wall and discuss:
Are most eight year olds in our class close to 130cm?
Does the tallest person in our class have the longest feet?