Mathematics

Beginner

50 mins

Teacher/Student led

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Learning Outcomes

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What you need:
Chromebook/Laptop/PC or iPad/Tablet
IWB/Projector/Large Screen

Negative Numbers in NI Winter Temperatures

Learn to read negative numbers on a thermometer, understand what minus means below freezing point, and compare cold temperatures using a vertical number line based on Northern Irish winter weather.

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1 What Does Minus Actually Mean?
2 Watching Negatives on a Thermometer
3 Place the Temperatures Together
4 Sketch the Thermometer in Your Jotter
5 Your Turn at the Thermometer
6 Why Is Minus 10 Smaller Than Minus 2?
7 What's Next
Pupil practice
Going further
Homework

1 - What Does Minus Actually Mean?

It was a cold morning in the Mournes last January. The BBC NI weather forecast showed minus five degrees Celsius, written as -5°C. What does that little minus sign actually mean? Is -5°C a real temperature, or just a way of saying 'very cold'?

In this lesson you will learn how to read negative numbers on a thermometer, place them in the right spot on a vertical number line, and compare two cold temperatures to see which is actually colder.

Teacher Notes

Open with a sketch of a thermometer on the IWB showing -5°C, or with a BBC NI weather screenshot saved earlier. Run a quick 90-second maths-talk: take three or four hands on 'what does the minus sign actually mean?'. Listen for ideas like 'below zero', 'colder than freezing', 'colder than the fridge'. Do not correct or confirm yet; the next step reveals the answer through the thermometer display.

👇 Mark your steps as done as you complete them.

+5 XP

2 - Watching Negatives on a Thermometer

Watch the two thermometers on the board. Each one is a number line stood up on its end, running from -20 at the bottom to +20 at the top. Zero sits in the middle, and that is the freezing point of water. Warmer temperatures live above zero. Colder temperatures live below.

On the first thermometer, notice the marker at -5°C. That is five degrees below zero, a cold morning in the Mournes. On the second thermometer there are two markers: one at -3°C and one at -8°C. Look carefully. -8°C sits further down the line than -3°C, because the further you go below zero, the colder it gets. The size of the negative tells you how far below zero you are.

Teacher Notes

Walk through each display in turn. On the first thermometer, point to zero and say 'this is freezing point'; then point to -5 and say 'five below freezing'. On the second, point to -3 first, then -8, then ask 'which is further from zero, and how do you know?'. Resist the urge to write any extra working; the try-together step is where pupils take the marker. Watch for the common misconception that -8 must be warmer because '8 is bigger than 3' and flag that you will come back to it in the wrap-up.

👇 Mark your steps as done as you complete them.

+10 XP

3 - Place the Temperatures Together

Now you take a turn at the thermometer. The line still runs from -20 at the bottom to +20 at the top. One pupil at a time will come up to the board to place a temperature the teacher calls out. The rest of the class predicts where the marker should go and calls 'higher' or 'lower' as it moves.

Once the class has placed five or six temperatures, the teacher will pick three of them and ask the class to read them off in order from coldest to warmest.

Class thermometer: -20 to +20

Teacher Notes

Call out temperatures one at a time and pick a different pupil to place each one on the IWB: -4°C, +7°C, -12°C, +18°C, -15°C, 0°C. As the marker moves, the rest of the class calls 'higher' or 'lower'. After all six are on the line, point to three of them (try -3°C, -10°C, +2°C) and ask the class in unison to read them coldest to warmest. Listen for pupils who say -3 is colder than -10; that is the headline misconception. Revoice using the thermometer: 'look how far -10 is below zero compared to -3'. Avoid writing the rule on the board yet; the maths-talk wrap names it.

+15 XP

4 - Sketch the Thermometer in Your Jotter

COPYBOOK MOMENT

In your jotter, sketch a vertical number line from -10 at the bottom to +10 at the top. Mark every whole number along the line and draw a little arrow at zero to show freezing point. Now mark four temperatures as the teacher calls them out:

Slieve Donard at 6am: -7°C
Belfast city centre: +2°C
your classroom right now: roughly +18°C
a freezer at home: about -18°C

Label each mark clearly with the place and the temperature.

One of these temperatures is colder than -10°C — when you get to it, add a little arrow pointing off the bottom of your line and write the temperature beside it.

Teacher Notes

Walk the room glancing at where pupils place each temperature. No marking; this is parallel-work accountability while the IWB build runs. Watch for two common slips: pupils marking -7 above zero because '7 looks like a big number', and pupils spacing the line unevenly so 0 ends up at the bottom. A whispered nudge is enough; do not stop the room. Note that -18°C lies off the bottom of a -10 to +10 line, which is a useful teaching moment: ask the pupil to add a small note 'off the bottom, much colder than -10'.

+10 XP

5 - Your Turn at the Thermometer

Work through the temperature challenges on the thermometer. One pupil at a time comes up to the board to place a temperature; the rest of the class predicts and calls 'higher' or 'lower' as the marker slides. Use the Check button to confirm before moving on to the next one.

If you finish the core set ahead of time, the extension challenges ask you to work out a new temperature from a starting value and a change. These are harder, so think before you place.

Place each temperature on the thermometer

Teacher Notes

Run the six core challenges as a whole-class IWB beat, with a different pupil at the board for each. The rest of the class does thumbs-up or thumbs-down before the pupil presses Check. Take a breath after challenge 3 (-12°C) to ask 'is -12 colder than -4? How do you know?', a quick maths-talk moment to lock in the size-of-negative rule. The extension bank requires pupils to compute a new value from a starting temperature and a change; reach for it only if the class has time. The homework bank is the at-home consolidation surface: same level as core, different numbers.

+15 XP

6 - Why Is Minus 10 Smaller Than Minus 2?

MATHS TALK

Think about

Everybody agrees that 10 is a bigger number than 2. So how can -10 be SMALLER than -2? Look back at the thermometer in your head.

-10 sits FURTHER BELOW zero than -2 does.
The further down the thermometer you go, the colder it gets.
So -10 is colder, lower, and smaller than -2, even though 10 is bigger than 2.

The minus sign flips the way size feels. With negatives, the bigger the number after the minus, the colder and the smaller.

On the thermometer, -10 is BELOW -2. Anything below another number is smaller. That's why -10 is smaller, even though 10 by itself is bigger than 2.

Teacher Notes

Display-only wrap. No typing, no individual answers to record. Take three or four raised hands and revoice the best 'further from zero' phrasing back to the whole class. Do not turn this into new teaching; it is a 3-minute close, not a sixth challenge. Keep the second thermometer from the model step visible while you discuss so pupils have the picture to point at.

+10 XP

7 - What's Next

Today you learned

Negative numbers sit below zero on a thermometer.
The further a negative is from zero, the colder and the smaller it is.
-10 is colder than -2 because it sits further below freezing.

Pupils complete activity-book page 7 during this lesson.

Coming up next

In the next lesson you will work out how much the temperature has CHANGED when it crosses zero, for example the rise from -3°C at dawn to +5°C by midday. You will count up through zero on the same kind of thermometer.

Teacher Notes

Pupils complete activity-book page 7 during this lesson. Hand out the activity-book page and circulate while pupils work. The access tier (4★) gives a vertical thermometer to read off and place temperatures; most pupils manage this independently. The stretch tier (3★★) introduces a colder country (e.g. -25°C in Russia) and asks pupils to extend the line. The challenge tier (2★★★) asks pupils to compare three temperatures with a written sentence using the words 'colder', 'warmer', 'further from zero'. Collect for marking against the answer book; flag any pupil who still places negatives above zero for a quick conversation next lesson.

+5 XP

Pupil practice

Module 1 · Number: Place Value, Negative Numbers and Order of Operations Number

Activity Book — Page 7

Lesson 7 · Negative Numbers in NI Winter Temperatures

Download Activity Book page (PDF)

Going further

Extension challenges

If you finish early — try these harder challenges on your device.

Number line

Practice at home

Homework

Device required

Tonight's homework — work through these on your device.

Number line

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Copyright Notice
This lesson is copyright of Coding Ireland 2017 - 2025. Unauthorised use, copying or distribution is not allowed.

Negative Numbers in NI Winter Temperatures

Teacher Class Feed

1 - What Does Minus Actually Mean?

2 - Watching Negatives on a Thermometer

3 - Place the Temperatures Together

Class thermometer: -20 to +20

4 - Sketch the Thermometer in Your Jotter

5 - Your Turn at the Thermometer

Place each temperature on the thermometer

6 - Why Is Minus 10 Smaller Than Minus 2?

Think about

7 - What's Next

Today you learned

Coming up next

Unlock the Full Learning Experience

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