Grade 3 (age 8-9)

Measuring Weight

Weight is the force with which the Earth pulls on an object. An apple feels heavier than a balloon, and we measure weight in grams or kilograms. A spring scale stretches more for a heavier object, while a balance scale stays level when both sides weigh the same. Change the weight to watch the spring stretch, and add weights to each side to see which is heavier.

What is Weight?

🤔 Feel the Weight

①Hold an apple and a balloon

②You feel the apple is heavier

③Weight = force of gravity pulling objects

④Units: g (gram), kg (kilogram)

Spring Scale

Object Weight50g

💡 How Spring Scale Works

①Heavier object → spring stretches more

②Length read = weight

③Read at eye level

④Always check the unit (g or kg)

Balance Scale

Left Weight30g

Right Weight50g

⚖️ How to Use Balance Scale

①Place object on one side, weights on the other

②Balanced = sum of weights = object weight

③Lighter side goes up

④Heavier side goes down

Summary

Meaning of Weight

Weight = force of Earth pulling object

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

Spring Scale

Heavier → spring stretches more

Length stretched → read scale → measure weight

Balance Scale

Balanced = both sides equal weight

Use weights to measure object precisely

🎯 Key Points

①Weight is the force of gravity

②Spring scale: stretch length = weight

③Balance scale: compare with weights

④Units: g, kg

⑤Same volume can have different weight

Examples and Unit Test

Example 1

On a spring scale, what happens to the length of the spring as you hang a heavier object?

On a spring scale, the heavier the object, the more the spring stretches.

So hanging a heavier object makes the spring stretch longer.

▸ The spring stretches more

A spring scale measures weight by how far the spring stretches (heavier = more stretch).

Example 2

On a pan balance, an apple is on the left and a weight on the right, and the left side goes down. Which is heavier?

On a pan balance, the heavier side goes down and the lighter side goes up.

Since the left side went down, the apple is heavier than the weight.

▸ The left side (the apple) is heavier

On a pan balance the heavier side goes down; if level, both sides weigh the same.

Unit-test style

Which statement about measuring weight is correct?

①Weight is the force with which the Earth pulls an object

②A spring scale stretches more when the object is lighter

③On a pan balance, the lighter side goes down

④The unit of weight is cm

⑤If a pan balance is level, one side is heavier

▸ ① Weight is the force with which the Earth pulls an object

Weight is the force with which the Earth pulls an object, and its unit is g or kg.

A spring scale stretches more when heavier (②), on a pan balance the heavier side goes down (③), the unit of weight is g or kg (④), and a level balance means both sides weigh the same (⑤).

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