Weight (Mass) • Topic 4 of 5

Practical Weight Measurement

Once units are clear, children learn to read real instruments. The simplest is the pan balance (or beam balance): two pans hang from a beam, the object goes in one pan and known weights in the other, and when the beam is level the object weighs exactly as much as the weights you added. The pan balance also teaches a quiet but important idea, transitivity, if a parcel balances a 1 kg weight, and a book also balances the same 1 kg weight, then the parcel and the book weigh the same. Beyond the pan balance, shops and kitchens use dial (spring) scales and digital scales. On a dial scale the needle points to the weight, and the trick is reading the small marks between the labelled kilograms, which often stand for 100 g or 50 g each, so a needle two small marks past 1 kg on a 100 g scale reads 1 kg 200 g. Good teaching here is built on estimate-then-check: a child first guesses ('this apple is lighter than half a kilogram, maybe about 150 g'), then weighs it and compares, which slowly sharpens a real feel for the units. Watch the classic confusions the syllabus flags: a kilogram of cotton and a kilogram of iron weigh exactly the same (only their volumes differ), and any weighing should account for the container, since the pan or bag has its own weight.

✅ Solved examples

1. On a pan balance, an onion balances perfectly against a 200 g weight in the other pan. The onion weighs:
Exactly 200 g. When the pans are level, the object equals the total of the standard weights on the other side.
2. A dial scale shows the needle resting on the second small mark after 1 kg, where each small mark is 100 g. The reading is:
1 kg 200 g. Two marks of 100 g each beyond 1 kg add 200 g, giving 1 kg 200 g (1200 g).
3. Which weighs more, 1 kg of cotton or 1 kg of iron, and why does this confuse learners?
Neither; they weigh the same, 1 kg each. Learners are misled because the cotton takes up far more space, but volume is not weight.
4. Before weighing, a teacher asks pupils to first guess an object's weight and then measure it. This teaching practice is called:
Estimation followed by verification (estimate-then-check). It builds number sense and a concrete feel for grams and kilograms.

✏️ Practice — try these, take hints as needed

1. If parcel A balances a 1 kg weight and parcel B also balances the same 1 kg weight, what can you say about A and B?
Both equal the same standard weight.
This is the idea of transitivity.
Parcels A and B weigh the same (both 1 kg).
2. A digital scale already reading 50 g (an empty bowl) shows 350 g after rice is added. The weight of the rice alone is:
Subtract the bowl.
350 minus 50.
300 g
3. On a pan balance, the pans are level. This means the two sides are:
Neither side dips.
Think equal.
Equal in weight

📝 Topic test — 8 questions

Auto-graded with full solutions; saved to your dashboard. Use the calculator and formula sheet (top-right) any time.

Loading questions…
← Unit Conversions Word Problems →