What is mass?
Mass tells us how heavy something is. We weigh light things in grams (g) and heavy things in kilograms (kg).
Key idea / 要点
1 kg = 1000 g. An apple is about 100 g. A schoolbag can be about 3 kg.
Comparing mass
The heavier object pulls the scale down more. A 5 kg bag is heavier than a 2 kg bag, because 5 is more than 2. We can also add masses together, or take one away, as long as we use the same unit for both.
Worked example / 例题
A melon is 4 kg. A pineapple is 1 kg. How heavy are they together?
Add: 4 + 1 = 5. Together they are 5 kg.
Remember / 记住
- Use g for light things, kg for heavy things.
- 1 kg = 1000 g.
- Read the pointer on the scale carefully.
- Bigger does not always mean heavier: a big pillow can be lighter than a small stone.