Time for Class 5

In this chapter, we dealt with time and the measurement of time. Certainly, time and its measurement are fundamental concepts in our understanding of the universe and daily life.

Time

Time is an interesting concept that shapes our day-to-day lives from the time we wake up in the morning to the time we go to bed at night. It helps us plan our day. Time is measured by either an analogue clock or a digital clock. An analogue clock and a digital clock are shown as:

Measurement of Time

The measurement of time is a fundamental concept that helps us understand and organize the passage of events. It involves quantifying the duration of various activities and occurrences.

Mostly, we use an analogue clock to measure time. A clock usually has a circular face with 12 numbers on it to help us tell the time. There are three hands inside the analogue clock:

1. The thin hand shows seconds.
2. The big hand shows minutes.
3. The small hand shows hours.

Two Formats of Time

Time can be expressed in two main formats: 12-hour format and 24-hour format. Understanding time in both the 12-hour and 24-hour formats is a valuable lesson.

A concise overview of both formats is as follows:

12-Hour Format:

In the 12-hour format, the day is divided into two segments: Ante Meridiem (AM) and Post Meridiem (PM).

→ AM ranges from 12:00 AM (midnight) to 12:00 PM (noon).
→ PM ranges from 12:00 PM (noon) to 12:00 AM (midnight).

The day's cycle in 12-hour format is represented as follows:

This format is commonly used on traditional clocks and watches. To tell time in the 12-hour format, we utilize numbers from 1 to 12, followed by "AM" or "PM" to denote morning, afternoon, evening or night.

24-Hour Format:

The 24-hour format also called the international time format divides the entire day into 24 hours. Hours extend from 00:00 (midnight) to 23:59 (just before the next midnight). It is a continuous time count without the need to switch between AM and PM.

The day's cycle in 24-hour format is represented as follows:

Examples for both formats of time:

→ 3:45 AM in the 12-hour format corresponds to 03:45 in the 24-hour format.
→ 3:45 PM in the 12-hour format is equivalent to 15:45 in the 24-hour format.

Both formats of time are indicated as:

Quarters of Time

A quarter of the time is a fraction of the time. So when we say “a quarter of time”, we are talking about four equal parts of time. Each part of time represents a quarter, as shown in the following figure:

Examples:

→ 9 o'clock indicates 9:00.
→ Quarter past 9 indicates 9:15.
→ Half past 9 indicates 9:30.
→ Quarter to 10 indicates 9:45.
→ 10 o'clock indicates 10:00.

Units of Time

Time is measured and represented using a range of units which are years, months, weeks, days, hours, minutes, seconds, etc.

Conversion of one unit to another unit

Here are some common units of time and how to convert between them:

Years to Months:

→ 1 year = 12 months
→ To convert from years to months, you need to multiply by 12.
→ For  example: 5 years = 5 years × 12
                                          = 60 months

Notes:

→ One month consists of 28, 29, 30 or 31 days depending on the month.
→ In a regular year, there are 365 days whereas a leap year has 366 days.
→ During a regular year, February has 28 days but during a leap year, it has 29 days.
→ A regular year contains 52 weeks and one extra day while a leap year contains 52 weeks and two extra days.

Weeks to Days:

→ 1 week = 7 days
→ To convert from weeks to days, you need to multiply by 7.
→ For  example: 5 weeks = 5 weeks × 7
                                            = 35 days

Days to Hours:

→ 1 day = 24 hours
→ To convert from days to hours, you need to multiply by 24.
→ For example: 5 days = 5 days × 24
                                        = 120 hours

Hours to Minutes:

→ 1 hour = 60 minutes
→ To convert from hours to minutes, you need to multiply by 60.
→ For example: 5 hours = 5 hours × 60
                                         = 300 minutes

Minutes to Seconds:

→ 1 minute = 60 seconds
→ To convert from minutes to seconds, you need to multiply by 60.
→ For example: 6 minutes = 6 minutes × 60
                                             = 360 seconds

Hours to Seconds:

→ 1 hour = 3600 seconds
→ To convert from hours to seconds, you need to multiply by 3600.
→ For example: 2 hours = 2 hours × 3600
                                         = 7200 seconds

Seconds to Centiseconds:

→ 1 second = 100 centiseconds
→ To convert from seconds to centiseconds, you need to multiply by 100.
→ For example: 51 seconds = 51 seconds × 100
                                               = 5100 centiseconds

Seconds to Milliseconds:

→ 1 second = 1000 milliseconds
→ To convert from seconds to milliseconds, you need to multiply by 1000.
→ For example: 12 seconds = 12 seconds × 1000
                                             = 12000 milliseconds

Minutes to Hours:

→ 1 minute = 1/60 hour
→ To convert from minutes to hours, you need to divide by 60.
→ For example: 420 minutes = 420 minutes ÷ 60
                                                 = 7 hours

Seconds to Minutes:

→ 1 second = 1/60 minute
→ To convert from seconds to minutes, you need to divide by 60.
→ For example: 600 seconds = 600 seconds ÷ 60
                                                 = 10 minutes

Seconds to Hours:

→ 1 second = 1/3600 hour
→ To convert from seconds to hours, you need to divide by 3600.
→ For example: 7200 seconds = 7200 seconds ÷ 3600
                                                     = 2 hours

Milliseconds to Seconds:

→ 1 millisecond = 1/1000 second
→ To convert from milliseconds to seconds, you need to divide by 1000.
→ For example: 12000 milliseconds = 12000 milliseconds ÷ 1000
                                                             = 12 seconds

Terms related to days

Let's explore some essential terms related to days:

1. 'Today' signifies the present day we are experiencing at this moment.
2. 'Yesterday' signifies the day before today. It is the day preceding today.
3. 'Tomorrow' signifies the day after today. It is the day following today.

Let's clarify with an example:

If today is Thursday, then yesterday was Wednesday and tomorrow will be Friday.

Example 1: How many minutes are there in a duration of 1 week, 3 days, and 4 hours? 

a) 14440 minutes
b) 14640 minutes
c) 15440 minutes
d) 15640 minutes

Answer: b) 14640 minutes

Explanation: Minutes present in 1 week 3 days 4 hours
= 1 week + 3 days + 4 hours
= 7 days + 3 days + 4 hours
= 10 days + 4 hours
=  (10 × 24) hours + 4 hours
=  240 hours + 4 hours
=  244 hours
=  (244 × 60) minutes
=  14640 minutes

Example 2: At 7:55 PM, Peru caught his train on Monday. He completed his journey in 30 hours and 35 minutes. What was the time at which he completed his journey?

a) 12:30 AM  on Tuesday
b) 1:30 AM  on Wednesday
c) 2:30 AM  on Wednesday
d) 3:30 AM  on Wednesday

Answer: c) 2:30 AM  on Wednesday

Explanation: Time at which Peru started his journey on Monday = 7:55 PM

Time at which Peru completed his journey = 7:55 PM (on Monday) + 30 hours + 35 minutes
                                                              = 7:55 PM (on Monday) + 24 hours + 6 hours + 35 minutes
                                                              = 7:55 PM (on Tuesday) + 6 hours + 35 minutes
                                                              = 1:55 AM (on Wednesday) + 35 minutes
                                                              = 2:30 AM  (on Wednesday)