Grade 4 (age 9-10)

Weight Measurement

Weight is how heavy an object is, and a pan balance measures it against small weights. When the two pans sit level, those weights equal the object's weight. Weight comes from gravity, so on the Moon it drops to a sixth while mass stays the same, and you slide the values to tip and level the balance.

Let's measure weight

Object weight50g

Weight piece30g

⚖️ Using a pan balance

①Place the object on the left pan

②Place weights on the right pan

③Adjust weights until level

④Sum of weights = the object's weight!

Weight and Mass

🌍 Weight vs. Mass

①Mass: amount of matter — same everywhere

②Weight: gravitational pull — varies by place

③On the Moon, weight is 1/6 of Earth's

④But mass is the same on Earth and Moon

Summary

Weight Measurement

When level: object weight = sum of weights

A pan balance gives precise weight

Weight Units

g (gram), kg (kilogram) — 1 kg = 1000 g

Common everyday units

Weight vs Mass

Weight (force) ≠ Mass (amount of matter)

Weight changes by place; mass is constant

🎯 Key Points

①Pan balance measures weight using weights

②Level means equal weight

③Units: g, kg

④Weight is the force from gravity

⑤Mass never changes by location

Examples and Unit Test

Example 1

On a pan balance, an object on one side balances the weights on the other. If the weights are 30 g and 20 g, what is the weight of the object?

When a pan balance is level, the weights on both sides are equal.

The weight of the object equals the sum of the weights placed, so 30 g + 20 g = 50 g.

▸ 50 g

When the balance is level, the weight of the object equals the sum of the weights.

Example 2

A person with a mass of 60 kg goes to the Moon. What happens to their weight and mass? (Moon gravity is 1/6 of Earth.)

Mass is the amount of matter in an object, so it does not change with location.

Weight is the pull of gravity, so on the Moon, where gravity is 1/6, the weight becomes 1/6 of that on Earth.

▸ Mass = 60 kg (unchanged) / weight = reduced to 1/6 of Earth

Mass is the same everywhere; weight differs by location depending on gravity.

Unit-test style

Which statement about weight and mass is correct?

①Mass changes when the location changes

②Weight is the pull of gravity

③On the Moon the mass of an object is reduced to 1/6

④If a pan balance is level, the object is heavier than the weights

⑤Weight and mass mean exactly the same thing

▸ ② Weight is the pull of gravity

Weight is the force of gravity pulling on an object, so where gravity differs, the weight differs too.

Mass is the same everywhere (① and ③), a level balance means equal weights on both sides (④), and weight is a force while mass is the amount of matter, so they differ (⑤).

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