In this unit we explore the size of a centimetre and measure objects using the centimetre rulers that we have constructed.
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:
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.
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?
Printed from https://nzmaths.co.nz/resource/all-about-me at 6:05pm on the 26th February 2021