Measuring, Time and Money
Primary 2 · Mathematics
Measuring, Time and Money
Lesson 1 of 3
12 min
Let's begin
Uwase and Byiringiro found a skipping rope at school.
Uwase says the rope is very long. Byiringiro says it is short.
Who is right? Guessing does not help. You must measure. Today you will learn how.
Uwase holds two pencils side by side.
She puts the bottom ends together. That is the rule: start both at the same place.
Now she looks at the top ends. One pencil sticks out higher.
That pencil is longer. The other one is shorter.
If you do not line up the ends, you will be tricked. A short pencil held high looks long!
Take a ruler. Look at the little lines.
The space from one number to the next number is one centimetre.
We write centimetre in a short way: cm.
Worked example
Byiringiro puts his pencil on the ruler.
The pencil starts at 0 and ends at 12.
So the pencil is 12 cm long.
Always start at 0, not at 1. The 0 is the starting line, like the start of a race.
Sometimes a thing sits in the middle of the ruler.
Worked example
A piece of chalk starts at 2 and ends at 9.
Do not say 9! Count the jumps from 2 to 9.
3, 4, 5, 6, 7, 8, 9. That is 7 jumps.
The chalk is 7 cm long.
You can also take away: 9 take away 2 is 7. Same answer.
Centimetres are small. Your classroom is very big.
For long things we use metres. We write it short: m.
One metre is 100 centimetres. That is a big step, about as wide as your arms open.
A pencil is measured in cm. A door is about 2 m tall. A classroom may be 6 m long.
Worked example
The skipping rope is 1 metre and 20 centimetres long. How many centimetres is that?
1 metre is 100 cm.
100 and 20 more make 120 cm.
So Uwase was right. The rope really is long!
Lift a stone in one hand. Lift a leaf in the other hand.
Your hand with the stone pushes down. The stone is heavier. The leaf is lighter.
But hands can be fooled. So we use a balance. It has two pans.
The pan that goes DOWN holds the heavier thing. The pan that goes UP holds the lighter thing.
Worked example
Keza puts a mango in one pan and a matchbox in the other.
The mango pan sinks down. The matchbox pan lifts up.
So the mango is heavier than the matchbox.
Worked example
Now she puts two same sweet potatoes, one in each pan.
The pans stay flat and level. Nothing goes down.
That means they weigh the same.
At the market, heavy things are weighed in kilograms. We write it short: kg.
A small bag of sugar is about 1 kg. A sack of beans is much more.
A feather is far too light for kilograms. Small and light, big and heavy.
Tip
Two tricks to remember
1. On a ruler, always start at zero. Zero is where the race begins.
2. On a balance, heavy things fall down. The pan that goes down is holding the heavier thing, just like your hand does.
Try each one on paper first, then tap Show answer to check.
What you learned today
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