Chapter notes: Time Travellers | Mental Maths - Class 1 PDF Download

How do we define Time?

What is a Clock?

A clock is used to measure time. A clock has two hands— the short hand called the hour hand and the long hand called the minute hand.

• An hour (h) and minute (min) are the standard units for the measurement of time.
• The hour hand shows the hour and the minute hand shows the minutes before and after the hour.
• The minute hand goes around the clock once in 1 hour. The hour hand goes around the clock once in 12 hours.
  
• When the minute hand moves all the way round the clock, i.e., from 12 to 12, an hour passes.

60 minutes = 1 hour  
1 day = 24 hours

Telling Time to the Half Hour

In the clock shown alongside, the hour hand is between 9 and 10 and the minute hand points to 6. The coloured part shows that the long hand or minute hand has moved half way round.
When the minute hand moves half way round the face of the clock, half an hour has passed and we say that it is half past nine.∴ Half past nine can also be written as 9:30.

60 minutes = 1 hour
30 minutes = One-half of an hour

Observe the following clocks

Telling Time to the Nearest Five Minutes

• When the hour hand (short hand) moves from one digit to the other, 1 hour passes.
• When the minute hand (long hand) moves from one digit to the other, 5 minutes pass.
  
• Count the minutes all around the clock by 5s, starting at 12.
  The numbers outside the clock show the count.
• So, we skip count by 5s to find the time to the nearest five minutes. There are many ways of reading and telling the time.
  

When the minute hand has moved past 6, we say the time in the following two ways:

1. First Way : The hour hand is between 4 and 5, so  the time is after 4 o’ clock. The minute hand is at 7. Starting at 12 and counting ahead by 5s to 7, we get 35 minutes. 

So, we say that the clock shows the time 35 minutes after 4 or 35 minutes past 4.

2. Second Way: The hour hand is between 4 and 5, so the time is before 5 o’ clock. The minute hand is at 7. Starting at 12 and counting back by 5s to 7, we get 25 minutes. We write 25 minutes to 5 to tell the time because there are 25 minutes left to 5 o’ clock.

Examples:

Telling Time to the Quarter Hour

Let us read time on the clocks given below:
The minute hand has moved one quarter (one-fourth) of the circle in moving from 12 to 3.So, 1 / 4 of an hour = 15 minutes.

• The time shown on the clock is 12:15 or Fifteen minutes past twelve, which we generally read as quarter past twelve.
  
• Both the clocks A and B given show the same time which can be read in clock A as: 8:45 or Forty-five minutes past 8.
• In clock B, the same time can be read as: Fifteen minutes to nine or Quarter to nine.

Examples: