3. Being resourceful
The previous activities should have shown your pupils that ‘standard units‘ of mass are needed because without these it is not possible to accurately compare or know how what the mass of something is. This next part explores how you can introduce terms and develop their understanding of kilogram (kg), and gram (g) (1000 gram = 1 kilogram). You may want to bring bags of sugar and rice to class, to show their mass is recorded in grams or kilograms and for them to feel the actual masses or make some mock ones i.e. plastic bags filled with sand, stones etc to the correct mass. If you can, borrow a pair of scales to do this.
If you do not have access to calibrated scales or masses at school, it may still be possible to make approximate measurements of mass using your simple balances, and using some every day objects that have their mass on them to test them against.
The second focus in this part is on understanding the terms gram and kilogram and being able to convert one to the other.
Case Study 3: Using homemade standard units
Mr Lokuruka wants his pupils to estimate, measure and compare the mass of objects in grams and kilograms. He asked permission from a secondary school science department to use their balances to make bean bags weighing 100 g, 50 g and 10 g (using different coloured cloth for each weight). He asked some of the parents who work in the local sewing shop to help him sew several sets for his class.
He demonstrated how to measure the mass of objects in grams using the improvised masses and a simple balance, and then asked pupils to measure the mass of objects to the nearest 10 g, and record their results in a table.
| Object | Mass |
|---|---|
| |
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The class were very enthusiastic and measured the mass of nearly everything they could find in the classroom. Mr Lokuruka listened to their talk as they did the activity and was pleased to hear them using the correct terms easily.
Key Activity: Measuring mass in grams
Before the lesson, collect a number of objects that have their mass shown – tinned or packet foods and other goods (you only need the wrapper, not the whole good). Try to have enough to give each group of pupils at least two or three labels. It would also be good to have some labels for mass in kilograms as well as grams.
Ask groups to write down the name of the product, and its mass – ensure that they include the correct units (grams or kilograms). They could do this by using the actual bags and putting them in order on their table. Pupils could arrange and re-arrange the packages by mass from highest to lowest or lowest to highest or sort into groups, e.g.:
- 0–250g;
- 250–500g;
- over 500g.
Then ask pupils to convert each weight from kilograms to grams or vice versa.
When they have finished ask each group to swap their sheets with another group and they can check each others answers. Remind them that 1,000 gram = 1 kilogram.
Discuss with your pupils why they might need to be able to convert mass in their everyday lives.
Display their work on the wall to show each group their achievements.
What did the groups learn and how do you know this? You could ask them to tell you what they think they have learned.
2. Introducing units to compare mass
