2
Balancing and the same mass
Learner’s Book 1: Unit 12, pp. 168–170
GoalUse heavier than, lighter than and the same as, and use equal cubes to balance scales.
New words
balance · when both pans have the same mass, so the scales stay levelheavier than · has more mass thanlighter than · has less mass thanthe same as · has equal mass
Explanation
Scales can tell us three things. One thing can be heavier than the other. One thing can be lighter than the other. Or both things can have the same mass. When the masses are the same, the pans stay level and we say the scales balance. We can use small cubes that are all the same to measure mass. If a pear balances 4 cubes, then the pear has the same mass as 4 cubes.
Worked examples
The sack of flour is in the left pan, and it goes down. The flour is heavier than the box of tea. The tea is lighter than the flour.
Both pans are level, so the scales balance. The cup has the same mass as 5 cubes.
An apple balances 3 cubes and an orange balances 5 cubes. Put both fruits in one pan. To balance them we need 3 cubes and 5 cubes in the other pan, which is 8 cubes.
Class activity
Cube balance: use 20 small things that are all the same (buttons or dried beans) as cubes. Find how many cubes balance a pencil case, a shoe and a spoon. Which one has the most mass? Put them in order.
Practice
1
The scales balance. Is the ball heavier than, lighter than or the same as 6 cubes?
the same as 6 cubes
2
A toy balances 6 cubes. A hat balances 3 cubes. How many cubes balance the toy and the hat together?
9 cubes (6 + 3)
3
Which pan has more mass, the left or the right?
the right
4
Fill in the word: a sparrow is ___ than a goat.
lighter