Weight (Mass) • Topic 2 of 5

Standard Units

Before reaching for grams, children weigh things in whatever is handy: marbles, erasers, identical wooden blocks or bottle caps. These are non-standard units. A pencil box might be 'as heavy as 8 marbles' for one child and 'as heavy as 5 stones' for another, and that mismatch is the whole point of the lesson. Because the chosen unit changes from person to person, the answers cannot be compared or trusted, so the world agreed on fixed, standard units of mass. The two that primary children use are the gram (g) for light things like a biscuit, a pencil or a packet of spice, and the kilogram (kg) for heavier things like a bag of rice, a watermelon or a school bag. A handy anchor: a one-rupee coin is roughly a few grams, a packet of sugar from the shop is one kilogram, and a small newborn baby is around three kilograms. For very heavy loads the quintal (100 kg) and the tonne (1000 kg) are used, for example weighing grain harvests or a truck, but day-to-day shopping stays in grams and kilograms.

✅ Solved examples

1. Two children weigh the same book using marbles and using erasers, and get different numbers. The lesson this is meant to teach is:
Non-standard units give different results for the same object, so we need fixed standard units (gram and kilogram) that everyone shares.
2. Which standard unit is most suitable for weighing a single biscuit, and which for a bag of potatoes?
A biscuit is weighed in grams (g) and a bag of potatoes in kilograms (kg). Grams suit light objects, kilograms suit heavy ones.
3. A shopkeeper weighs a sack of wheat for a farmer and records 1 quintal. How many kilograms is that?
1 quintal = 100 kg. The quintal is a standard unit used for heavy loads such as grain.

✏️ Practice — try these, take hints as needed

1. Why are marbles or erasers called non-standard units of weight?
Their size is not fixed for everyone.
Different objects give different counts.
Because they are not fixed in size, so the same object gives different measures, making results unreliable.
2. Name the standard unit you would use to weigh a watermelon.
It is a fairly heavy fruit.
Not grams.
Kilogram (kg)
3. A tonne is a standard unit used for very heavy things. One tonne equals how many kilograms?
Same number as grams in a kilogram.
It is 1000.
1 tonne = 1000 kg

📝 Topic test — 8 questions

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