Introducing negative numbers: below zero on the number line
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Learning Objectives
- 1Read and write negative whole numbers using the minus sign
- 2Place negative numbers correctly on a horizontal number line
- 3Compare and order numbers that include both negatives and positives
- 4Use negative numbers to describe real situations like temperature and depth
Mini Lesson
Numbers do not stop at zero. Below zero you find a whole new set of numbers called negative numbers. They show things that go below a starting point - cold temperatures, depths underwater, money owed, or floors below the ground floor in a lift.
What Is a Negative Number?
A negative number is a number less than zero. We write it with a minus sign in front, like -3 or -12. Read -3 as "negative three" or "minus three". Positive numbers are greater than zero; we sometimes write +5 to make it clear, but most of the time we just write 5.
- Positive: 1, 2, 3, 4, 5, ...
- Zero: 0 - the dividing point
- Negative: -1, -2, -3, -4, -5, ...
- Negatives go on forever, just like positives.
The Number Line Goes Both Ways
Picture a horizontal number line. Zero sits in the middle. Positive numbers go to the right and grow larger. Negative numbers go to the left and grow more negative - they get smaller. Each step left or right is the same size, so -3 is exactly three steps left of zero.
- Find zero in the middle
- Count steps to the right for positive numbers (+1, +2, +3, ...)
- Count steps to the left for negative numbers (-1, -2, -3, ...)
- A number on the LEFT is always SMALLER than a number on the RIGHT
Comparing Negatives Can Trick You
With negatives, the rule "bigger digit means bigger number" flips. -2 is GREATER than -8, because -2 is closer to zero. Think of temperature: -2 degrees is warmer than -8 degrees. The colder the temperature, the more negative the number.
- -2 > -8 (negative two is greater than negative eight)
- -1 > -100 (negative one is greater than negative one hundred)
- 0 > -1 (zero is greater than every negative number)
- Any positive > any negative (5 > -50)
Where We See Negative Numbers in Real Life
- Temperature: a winter day might be -7 degrees Celsius
- Elevation: the Dead Sea is about -430 meters (below sea level)
- Money: an account that owes 20 dollars is at -20
- Lifts: the basement floor might be labeled -1
- Sport: a golf score of -3 means three under par
Tip: when you see a minus sign in front of a number, picture jumping LEFT on the number line. The bigger the jump, the more negative you go.
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