## Time and Temperature

**Time**

Telling time on an analog clock can pose a challenge for many students. Students who have difficulty distinguishing between “clockwise” and “counterclockwise” rotation may be helped by explaining to them that the numerals on the face of the clock increase in a **clockwise** direction.

It is important to mention that the numerals on a clock face are used to measure two distinct time scales. The numerals 1 to 12 divide the circular face of a clock into 12 equal sectors. Because the minute hand rotates through these 12 sectors in 60 minutes, each sector corresponds to 5 minutes. As a result, if the minute hand is pointing to the numeral N, the time is 5N minutes past the hour indicated by the hour hand. For example, if the hour hand is just past the 7 and the minute hand is at 2, the time is **10 minutes after 7, or seven ten.** Special attention should be given to N = 3 and N = 6. When the minute hand reaches these numerals, expressions such as **quarter past seven** and **half past seven** as well as **seven fifteen** and **seven thirty,** respectively, are used.

Telling minutes before the hour can be more challenging. For 1 ≤ K ≤ 11 and 1 ≤ N ≤ 11, the underlying rule is

5N minutes after Kis the same as5(12 – N) minutes before K + 1.

In practice, this rule tends to be applied only for N = 8, 9, 10, and 11, and as a practical matter, children should be taught to associate these values of N with a certain number of **minutes before the hour** by memory. Especially important is N = 9, which leads to **a quarter to** as well as **15 minutes before.**

At this grade level, determining elapsed time is limited to simple problems that do not require crossing noon. Students use an analog clock to determine the elapsed number of minutes between two times.

A study of the calendar at this grade level should reinforce skills that have been mastered. Studying the calendar also provides for a review of ordinal numbers.

**Temperature**

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

Temperatures below zero are recorded as negative integers. Students will learn about integers in future grades.

In the metric system, temperature is measured in degrees Celsius. On the Celsius scale, water boils at 100° C and freezes at 0° C. Normal human body temperature is 37° C.

**Teaching Model 12.7:** Temperature: Degrees Fahrenheit and Celsius