Negative numbers: below zero
📖 In short
In winter the weather presenter might say: “Tonight it will be minus five.” How can there be a number smaller than zero? These are negative numbers, written with a minus sign in front: −5. We find them in cold weather, in floors underground and in the depths of the sea.
🤩 Did you know?
- The coldest temperature ever recorded on Earth was in Antarctica: about −89 degrees.
- The Dead Sea is the lowest place on land: about −430 meters below sea level.
- Fresh water freezes at 0°, and salty sea water at about −2°.
- Scholars in China and India used negative numbers more than 1300 years ago to keep track of debts.
🔎 Find out more
🌟 The number line keeps going
When we draw the number line, zero isn't its start! On its right are the positive numbers 1, 2, 3…, and on its left the negative numbers −1, −2, −3… Every negative number is like a positive number seen in a mirror.
🔍 The thermometer
When it gets very cold, the liquid in the thermometer drops below zero. −10° is colder than −2°, because it's further below zero. At the South Pole the temperature can reach −80°!
💡 Lifts and floors
In a lift we see floor 0, the ground floor, then 1 and 2 going up. But an underground car park might be on floor −1 or −2.
🎯 Which is bigger?
The further a negative number is from zero, the smaller it is. So −3 is bigger than −7. And every positive number is bigger than every negative number: 1 is bigger than −1000!
📊 See it in a picture
🧮 Worked examples
- −3 < 2Every negative number is smaller than every positive number.
- −8 < −2−8 is further left of zero, so it's smaller.
- 3 − 5 = −2From 3 we go back 5 steps on the line and land on −2.
📚 Key words
- Negative number
- A number smaller than zero, written with a − sign in front
- Positive number
- A number bigger than zero
- The thermometer
- A tool for measuring temperature
🧪 Try it at home
Put a thermometer in the fridge, then in the freezer. What does it say each time? Which place is below zero?
🧩 Test yourself
1 Which is colder: −10° or −3°?
2 Where is floor −1?
3 What is 2 − 5?