Level 1 · Ages 6–8
Read it again any time, including while you work through the exercises.
Hold a book in one hand and a feather in the other. You feel right away that the book presses down harder: we say it is heavier. This feeling of heavy or light is the object's mass. Your hands are your very first scale!
But your hands can be fooled when two objects feel similar. To compare without mistakes, we use a real balance scale: put one object on each side, and the pan that goes down carries the heavier object. If both pans stay level, the two objects have the same mass.
To say exactly how much an object weighs, we use two units: the gram (g) for light things, and the kilogram (kg) for heavy things. A paperclip weighs about 1 g, an apple about 150 g, and a big dictionary about 1 kg.
Remember the magic link between them: 1 kg = 1000 g. One thousand grams fit inside a single kilogram! Thanks to this link, you can compare masses even when they are not written in the same unit. Your turn!
Which is heavier: a 1 kg bag of flour or an 800 g pack of rice?
1 kg = 1000 g
I put both masses in the same unit: I turn the kilogram into grams.
1000 g > 800 g
Now I can compare the numbers: 1000 is greater than 800.
Result: The 1 kg bag of flour is heavier.
On a balance scale, a melon balances two weights placed together: 500 g and 200 g. How much does the melon weigh?
melon = 500 g + 200 g
The pans are level: the melon therefore weighs as much as the two weights together.
500 + 200 = 700
I add the two weights to find the melon's mass.
Result: The melon weighs 700 g.