2
Grams or kilograms?
Discover Mathematics P2: Term 1, Lessons 41–50
GoalChoose grams or kilograms as the best unit to weigh an object.
New words
mass · how heavy something isgram (g) · a small unit of masskilogram (kg) · a big unit of massheavy · has a lot of mass
Explanation
We measure how heavy things are with units of mass. For light things we use grams, written g. A paper clip is about 1 g and a feather is only a few grams. For heavy things we use kilograms, written kg. At the market, tomatoes are sold by the kilogram. A bag of rice is 1 kg. A watermelon is several kg. A kilogram is a much, much bigger unit than a gram. Ask yourself: is it light enough to hold with two fingers? Then use grams.
| Unit | Use it for | Examples |
|---|---|---|
| g | light things | paper clip, feather, egg |
| kg | heavy things | bag of rice, watermelon, school bag |
Worked examples
A paper clip is very light. We weigh it in grams. It is about 1 g.
A watermelon is heavy. We weigh it in kilograms, not grams.
The two pans of this balance hold the same mass, 10 g each, so the balance stays level.
Class activity
Light or heavy basket. Collect 8 things from the home, for example a spoon, a coin, a pillow, a school bag, a bag of rice, a sock, a pencil, a bottle of water. Put them in two baskets: ‘weigh in grams’ and ‘weigh in kilograms’. Hold them in your hands to feel the mass.
Practice
1
Which unit is best for an egg: g or kg?
g (grams).
2
Which unit is best for a watermelon: g or kg?
kg (kilograms).
3
Which unit is best for Omar’s school bag: g or kg?
kg.
4
Which unit is best for a feather: g or kg?
g.
5
The left pan holds 3 kg and the right pan holds 5 kg. How many kg more is the right pan?
5 − 3 = 2 kg more.