We measure: metre, litre, kilogram · البرمجة مع مارتن

Measure, pour, weigh

Numbers do not live only in questions. They also say how long something is, how heavy it is and how much fits where. For that they need units.

A metre measures length. How tall you are, how long the room is. Small things are measured in centimetres — a metre has 100 centimetres.

A litre measures liquids. How much water is in a bottle, how much milk is in a carton.

A kilogram measures weight, people call it a kilo. How much a bag of potatoes weighs, how much you weigh.

You meet units everywhere. A recipe wants half a litre of milk. A doctor measures your height in centimetres. A seller weighs apples in kilos. A road sign counts kilometres. Grown-ups talk in units all day — and today you will start to understand them. On top of that you will try it all: you will measure, pour and weigh for real.

A number without a unit is half the information. “I measure 120” — of what? Fleas? Centimetres! Always say the number and the unit.

Adam bakes gingerbread with dad. “Hand me half a litre of milk and a kilo of flour,” dad reads from the recipe. Adam pours milk into a measuring jug to the 0.5 l mark. He tips flour onto the scales until they show 1 000 grams. “Dad, a kilo is a thousand grams?” “Exactly.” Then they measure the tin: 30 centimetres. “All cooking is measuring,” dad laughs. In the evening Adam measures himself with a tape too: 126 centimetres. “That is a metre and 26 centimetres extra!” He writes the number in pencil on the door frame. “In a year you will measure again,” dad promises. “The difference will say how much you have grown.”

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Length = metres and centimetres. Liquid = litres. Weight = kilograms. If you do not know, picture what you would measure the thing with: a tape, a jug, or scales?

Three units and how to count with them

How to measure length. Put a ruler or a tape with zero at the start of the thing. Read the number at the end. A pencil from zero to the number 14 → the pencil is 14 cm. A metre has 100 cm — anyone who measures more than 100 cm measures more than a metre.

How to estimate. Before you measure, take a guess. A door? About 2 metres. A milk carton? 1 litre. A bag of potatoes? Maybe 5 kilos. Guess, then measure — that is how you find out how good your eye is.

Counting with units. You can add and subtract only the same units:

2 litres of juice and 3 litres of water = 5 litres of liquid.
Shopping: 2 kg of apples and 3 kg of potatoes = 5 kg in the bag.
A string 40 cm and a string 30 cm = 70 cm.

You cannot add litres with kilograms — that is like adding apples with songs.

Anchor points so you have a picture: a big bottle of water = 1.5 litres. A carton of milk = 1 litre. A pack of flour or sugar = 1 kilo. Your step = about half a metre. A grown-up’s thumb = about 1 cm across.

The table is 75 cm high. Is it higher than a metre?

A metre has 100 centimetres.

I compare: 75 and 100. Tens: 7 against 10. A hundred is more.

75 < 100, so the table is lower than a metre.

By how much? 100 − 75: from 75 to 80 is 5, from 80 to 100 is 20. Together 25. The table is 25 cm lower than a metre.

Into the soup you put 1 litre of water and then 2 more litres. How much is in the pot?

Same units — litres with litres. I can add.

1 + 2 = 3 litres.

And the other way: if 1 litre boiled away, 3 − 1 = 2 litres would be left.

Always write the unit with the result. “3” is not an answer. “3 litres” is an answer.

The bag can hold 10 kilos. You carry 4 kg of potatoes and 3 kg of apples. Will 5 kg of flour still fit?

I add what is already in the bag: 4 + 3 = 7 kg.

I add the flour: 7 + 5 = 12 kg.

I compare with what it can hold: 12 > 10.

It will not fit. The bag would carry 12 − 10 = 2 kilos more than it can. I take the flour in a second bag, or I buy less of it.

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Do not add different units. 2 litres + 3 kilos is not 5 of anything. First look if you are counting the same things: length with length, litres with litres, kilos with kilos.

Practice: now you do it 🎲

Now try it for real. You will see all the questions at once, like on paper. البداية with ten. If it goes well, add more.

Convert metres and centimetres. A number without a unit.

Practise the questions

On paper

Paper, a pencil, a ruler or a tape measure. And the kitchen.

Measure three things on the table (a pencil, a book, a mug) and write the lengths in centimetres.
Find three things in the kitchen with litres or kilograms on the pack. نسخ them with the unit.
First guess, then measure: how wide is the table? Write the guess and the real width.
Calculate: in the basket there are 3 kg of apples and 2 kg of pears. How many kilos are you carrying?

Now you 💪

I know what a metre, a litre and a kilogram measure.
I can measure a thing with a ruler from zero.
I add only the same units and I write the unit with the result.

✅

Done when: You measure three things, find litres and kilos in the kitchen and calculate the bag question.

What to take from this lesson

A metre measures length, a litre liquids, a kilogram weight.
1 metre = 100 centimetres. 1 kilo = 1000 grams.
A number without a unit is half the information.
You can only add the same units.
First guess, then measure. That trains your eye.