Going below zero to understand negative numbers and their place on the number line.
Have you ever wondered how a pilot knows they are flying high enough, or how a submarine captain knows they've gone too deep? In the world of math, zero isn't the end—it's just the beginning of a whole new direction!
In your math journey so far, you've mostly used whole numbers starting from . But sometimes, we need to go below zero. Integers are the set of whole numbers and their opposites. This includes positive numbers (), negative numbers (), and zero. Zero is special because it is neither positive nor negative—it is the 'neutral' starting point. We use negative numbers to describe things like being in debt, temperatures below freezing, or depths below sea level.
Quick Check
If a bird is flying feet above the water and a fish is swimming feet below the surface, what integer represents the fish's position?
Answer
A number line is like a map for integers. On a horizontal line, positive numbers live to the right of zero, and negative numbers live to the left. On a vertical line (like a thermometer), positives are above zero and negatives are below. The further a number is to the right (or higher up), the larger it is. Even though is bigger than , is actually smaller than because it is further away from zero in the negative direction.
Let's place the following integers on a horizontal number line: .
1. Draw a line and mark in the center. 2. Move units to the right of and mark it as . 3. Move units to the left of and mark it as . 4. You can now see that is the furthest left, making it the smallest value.
Quick Check
On a vertical number line, is higher or lower than ?
Answer
Lower
To compare integers, we use inequality symbols: (greater than) and (less than). A helpful trick is to remember that the symbol always 'eats' the larger number. On a number line, any number to the right is always greater than any number to its left. This means that any positive number is greater than any negative number. For example, because is to the right of .
Compare the depths of two submarines. Submarine A is at meters and Submarine B is at meters. Which one is closer to the surface?
1. The surface is . 2. Compare the two values: and . 3. Since is further to the right on a number line (closer to ), . 4. Submarine A is closer to the surface.
Order these temperatures from coldest to warmest: .
1. Identify the negative numbers: . 2. Find the smallest (most negative): . 3. Arrange the rest moving right on the number line: . 4. Add zero and the positive number: . 5. Final order: .
Which integer represents a bank withdrawal of $\$45$?
Which of the following statements is true?
Zero is a positive integer.
Review Tomorrow
Tomorrow morning, try to think of three things in your house that could be represented by negative numbers (like the temperature in the freezer!).
Practice Activity
Draw a vertical number line from to and mark your favorite number, the current temperature, and the number of siblings you have.