Measures of Time
6th Maths : Term 2 Unit 2 : Measurements
The procedure of measuring time has undergone several changes from ancient period.
Measures of Time
The teacher asks students to answer the following questions:
- 1. How long do you take to run 100 metres?
- 2. How long do you take to walk one kilometer?
- 3. What is the time taken for a cup of rice to be cooked?
- 4. What is the cultivation period of groundnut?
These questions will help us to find the importance of time in our day-to-day life. Now let us discuss the development of measures of time.
The procedure of measuring time has undergone several changes from ancient period. Initially, a stick in the sand was used to measure time by measuring the length of the shadow of that stick. Then horizontal and vertical plates were used as sundials to measure time between sunrise and sunset, that is in the day time. Firing of knotted ropes was used to measure time in the darkness. The approximate time taken for the fire to travel from one knot to other formed the part of night. In later days, a day was divided into 24 equal parts (hours) of which 12 hours were for daytime and 12 hours were for night time approximately.
Time taken by the Earth to complete one full rotation around the Sun is known as the Solar Year. It was divided into 12 equal parts which is known as the Solar month. The duration between two full moons is known as the lunar month and 12 lunar months are known as lunar year. But we follow solar year and month.
Various clocks had been designed and used to measure time from different parts of world, like water clock, sun dial candle clock, sand clock, rope clock, etc. Have you seen those clocks? Look at the clocks shown below.
Study of devices that are measuring the time is called ‘HOROLOGY’.
Nowadays, we use pendulum clock, digital clock, quart clock, atomic clock to find time accurately.
Our Tamil people were experts in the Astronomical science. The Tholkappiam deals the pozhuthu (time). They divide a day into six major divisions, together called “Sirupozhuthu (சிறுபொழுது)”. A year into six major divisions, together called “Perumpozhuthu (பெரும்பொழுது)”.
1 Nahigai = 24 min; 1 hour = 2.5 nazhigai = 1 Orai; 1 day = 24 hours = 60 nazhigai
Unit of Time: Today we are measuring time accurately. The units of time are second, minute, hour, day, week, month, year, etc. They are interrelated.
Recap: 1. Read and write the time in the appropriate place.
1. Reading the time:
Practise to say time in two ways:-
Practise to say the time using "past"
Practise to say the time using "To"
Say the following time in two ways:
a) 9.20: 20 minutes past 9; 40 minutes to 10
b) 4.50: 50 minutes past 4; 10 minutes to 5
c) 5.15: 15 minutes past 5; 45 minutes to 6
d) 6.45: 45 minutes past 6; 15 minutes to 7
e) 11.30: 30 minutes past 11; 30 minutes to 12
2. Conversion of Time
Calculation of time to the nearest seconds is very essential in some situations like launching rocket, running race, arrival and departure. So, we need to know the conversion of time. Let us remember the time related chart as follows:
Solution:Time = 3 hours and 35 minutes
= (3 × 60) minutes + 35 minutes
= 180 minutes + 35 minutes = 215 minutes
Solution:
= (7 × 60 × 60) seconds + (16 × 60) seconds + 20 seconds
= 25200 + 960 + 20 = 26,180 seconds
i) 4 hours = 240 minutes
ii) 240 minutes = 4 hours
iii) 30 minutes = 1800 seconds
iv) 3600 seconds = 1 hours
v) 2 hours = 7200 seconds
3. Ordinary Time or the 12-Hour Format
The 12 hour clock has antemeridien (a.m) and postmeridien (p.m). Exactly 12.00 at night is midnight; 12.00 at day is noon.
- a.m: After 12:00 midnight and before 12:00 noon.
- p.m: After 12:00 noon and before 12:00 midnight.
4. Railway Time or the 24-Hour Format
Railways, Airways, and Defence use 24 hour clock. Usually denoted in 4 digits. First two digits: hours, last two: minutes. 5 p.m = 17:00 hours.
12 midnight = 00:00 or 24:00 hours. 12 noon = 12:00 hours.
5. Conversion of Time Formats
To convert 12h to 24h: Add 12:00 to any hour from 01.00 p.m. To convert 24h to 12h: Subtract 12:00 from any hours from 13:00 hours.
6. Duration between two time instances
Solution: 16:00 - 06:00 = 10 hours.
(iv) Total journey time = 8 hours.
7. Year & Leap Year
A year takes 365 days 6 hours. Every 4th year has 366 days (Leap Year). February has 29 days in a leap year.
Identification: Divisible by 4. Centuries must be divisible by 400.
Silver: 25th | Ruby: 40th | Golden: 50th | Diamond: 60th | Sapphire: 65th | Platinum: 70th
1 Decade = 10 years | 1 Century = 100 years | 1 Millennium = 1000 years.