# 2. Introducing units to compare weights

When developing understanding of the idea of weighing it is better if non-standard units are used to measure first. If pupils compare and contrast weights against non-standard unit bottle tops or beans they will quickly understand this is not sensible as the weight of different bottle tops and seeds vary. This is made easier by making sure they have sufficient experience weighing objects against different non-standard units.

Only when pupils understand the need for a common unit should the introduction of standard units like grams or kilograms begin.

## Case Study 2: Using a ‘standard’ unit to measure

Lizzy, a Primary school teacher, felt that having taught her pupils how to use a simple balance to compare weights of objects, they should now compare the weight of any object with that of a given chosen ‘standard’ object.

She assembled different objects and chose dry beans to be her chosen measure. Using the balance she asked two pupils to place an object on one pan and put enough beans on the other until it balanced. They counted the beans for each object and recorded their results.

Next she used some longer beans and weighed the same objects and recorded these results. She talked with the class about the difference in numbers between the two kinds of bean and how difficult it was to compare the weight of a stone and wood if one person used one set of beans and the other used the bigger beans.

## Activity 2: Data presentation

Before doing this, read Resource 3: Pupil instructions for weighing activity and collect together the following resources – enough for your size class.

• simple balances
• collect objects of similar weights to use as measures (e.g. bottle tops and beans)
• objects of different weights to measure (e.g. small bottles, tins or stones).

You could just collect enough for one group and have each group take turns to do the activity while the others do different work.

Write the instructions for the groups on the board and explain what they have to do.

Resource 4: Traditional weights used in Ghana. These are examples of Akan weights used in trading. Notice that they are fashioned very beautifully.

(See Key Resource: Using group work in the classroom [Tip: hold Ctrl and click a link to open it in a new tab. (Hide tip)] )

At the end, ask them to compare how it was different using beans or bottle tops to measure the weight, rather than just comparing pairs of objects. Note their answers on the board. Ask if they think this is a fairer way to measure.

Ask pupils to list the objects in order from heaviest to lightest – is this harder or easier than before? Why?

1. Doing practical work in groups

3. Being resourceful