Chapter 12: Ticking Clocks and Turning Calendar

Tick, tock, tick, tock... Time never stops. We catch it using clocks and calendars. Today, let's master both.

What we'll learn

• Read time in hours and minutes.
• Use am and pm, and the 24-hour clock.
• Calculate duration between two times.
• Read calendars and count days, weeks, months.

The big idea

A clock has three hands. The hour hand is short, the minute hand is long, and the second hand is the thinnest and fastest.

1 hour = 60 minutes. 1 minute = 60 seconds. 1 day = 24 hours.

We use am for time before noon (12 midnight to 12 noon) and pm from noon to midnight. So 7 am is breakfast time, 7 pm is dinner time.

In the 24-hour clock, instead of saying "1 pm", we say "13:00". Add 12 to any pm time to convert. So 4 pm = 16:00. Railway stations and airports love the 24-hour clock , no confusion!

To find duration, subtract the smaller time from the bigger one. From 2:15 pm to 4:45 pm = 2 hours 30 minutes.

A calendar shows days, weeks and months. 7 days = 1 week. 12 months = 1 year. February has 28 days (29 in a leap year). Months with 31 days: Jan, Mar, May, Jul, Aug, Oct, Dec. The rest have 30, except Feb.

Explore with examples

1. The time is 3:45. What does each hand show?

The hour hand is between 3 and 4. The minute hand points to 9 (because each number is 5 minutes; 9 × 5 = 45).

2. Convert 5:30 pm to 24-hour time.

5 + 12 = 17. So 17:30.

3. How long from 9:20 am to 11:50 am?

11:50 − 9:20 = 2 hours 30 minutes.

4. Your birthday is 15 August (Independence Day). Today is 10 August. How many days till your birthday?

15 − 10 = 5 days.

Hands-on activities

Clock Story

Note the times of 5 things you do today , waking up, eating, going to school, returning, sleeping. Write each as a clock time and as 24-hour time.

Stopwatch Race

Use a stopwatch (phone). Time how long you take to write your full name 10 times. Then to do 20 jumps. Compare.

Calendar Hunt

Open this year's calendar. Find: which day was your last birthday? Which day will be Independence Day this year? How many Sundays in July?

Try it yourself

1. Convert 9 pm to 24-hour time.
2. 1 hour = ? minutes. 1 day = ? hours.
3. From 7:15 am to 8:00 am , how many minutes?
4. Which month has the fewest days?
5. If today is Wednesday, what day is 10 days later?
6. The bus leaves at 14:45 and arrives at 17:20. How long?
7. How many seconds in 5 minutes?

Recap

• Three hands: hour, minute, second.
• am = before noon; pm = after noon.
• 24-hour clock removes confusion (add 12 to pm times).
• 7 days = 1 week, 12 months = 1 year.