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Grade 3 (age 8-9)

grade 3 Measuring Weight

Hold an apple in one hand and a blown-up balloon in the other, and even though the balloon is bigger, the arm holding the apple feels heavier. Weight is how strongly the Earth pulls on an object, and in everyday life we give it in g (grams) or kg (kilograms). A spring scale uses the fact that a spring stretches steadily more as heavier objects hang from it, and a balance scale uses the fact that its beam sits level when both sides weigh the same. In the first picture, change the weight of an object and watch how far the spring stretches; in the second, change the weights on the two pans and see which way the beam tips.

What is weight?

🤔 Feel the weight
①Bigger does not always mean heavier: a small apple weighs more than a blown-up balloon
②Weight is how strongly the Earth pulls on an object
③Things fall when you let go of them because the Earth pulls on them
④In everyday life we give weight in g (grams) and kg (kilograms), and 1 kg is 1000 g

Weighing with a spring scale

50g
💡 How a spring scale works
①The heavier the hanging object, the more the spring stretches
②When the weight doubles, the stretch doubles too, so the stretch tells you the weight
③Read the mark the pointer shows from straight in front, with your eyes level with it
④Each scale has a limit, and hanging something too heavy can ruin the spring

Comparing with a balance scale

30g
50g
⚖️ How to use a balance scale
①First check that the beam is level when both pans are empty
②Put the object on one pan and weights you know on the other
③The heavier pan goes down and the lighter pan goes up
④When the beam is level, the weights added together equal the weight of the object

Summary

What weight is
Weight = how strongly the Earth pulls on an object
The units are g (grams) and kg (kilograms), and 1 kg = 1000 g
Spring scale
Heavier → the spring stretches more
Read the stretch from the scale marks to find the weight
Balance scale
Level beam = both sides weigh the same
Compare the object with known weights to find its weight
🎯 Key points
①Weight is how strongly the Earth pulls on an object
②A spring scale finds weight from how far its spring stretches
③A balance scale finds weight by comparing with known weights, and a level beam means both sides are equal
④We use g and kg as units of weight
⑤Two things of the same size can have different weights

Examples and Unit Test

Example 1
What happens to the length of the spring when you hang a heavier object on a spring scale?
1
On a spring scale, the heavier the hanging object, the more the spring stretches.
2
So a heavier object stretches the spring longer, and the pointer shows a bigger number.
▸ The spring stretches longer
In the first picture, raising the weight from 50 g to 100 g doubles how far the spring stretches.
Example 2
You put an apple on the left pan of a balance scale and a weight on the right pan, and the left pan went down. Which side is heavier?
1
On a balance scale, the heavier pan goes down and the lighter pan goes up.
2
The left pan went down, so the apple is heavier than the weight.
▸ The apple on the left is heavier
To find the apple's weight, keep adding weights on the right until the beam is level.
Unit-test style
Which statement about measuring weight is correct?
①Weight is how strongly the Earth pulls on an object
②A spring scale stretches more the lighter the hanging object is
③On a balance scale, the lighter pan goes down
④We use cm as a unit of weight
⑤When a balance scale is level, one side is heavier
▸ ① Weight is how strongly the Earth pulls on an object
1
Weight is how strongly the Earth pulls on an object, and we use g or kg as its units.
2
A spring scale stretches more for heavier objects (②), the heavier pan of a balance scale goes down (③), units of weight are g and kg (④), and a level beam means both sides weigh the same (⑤).
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