## Time and Temperature

**Time**

When adding or subtracting denominate numbers involving time, students must remember that there are 24 hours in a day, 60 minutes in an hour, and 60 seconds in a minute. When finding elapsed time, it is also important for them to notice whether the times given are a.m. or p.m.

**Temperature and Negative Numbers**

The set of integers consists of the counting numbers 1, 2, 3, …, their opposites ^{−}1, ^{−}2, ^{−}3, …, and the number 0. In this chapter, students are introduced to negative numbers as they are used to record temperatures below 0. The integers can be represented on a number line that extends both to the left and to the right. The positive integers are represented to the right of 0 and the negative integers are represented to the left of 0.

Thermometers are used to measure temperature. Children may think of a thermometer as a vertical number line. In the customary system of measurement, temperature is measured in degrees Fahrenheit. In the metric system of measurement, temperature is measured in degrees Celsius. On the Fahrenheit scale, water boils at 212°F and freezes at 32°F. Normal human body temperature is 98.6°F. On the Celsius scale, water boils at 100°C and freezes at 0°C. Normal human body temperature is 37°C.

At this grade level, students use the number line or a thermometer for finding the difference between two temperatures. Computation with negative integers is not covered in this grade.

**Teaching Model 13.2:** Elapsed Time