time measurement

Time may be defined as the gap or interval between two events. The standard unit for measuring time is second. The larger units of time are minutes, hours, days, months, and years. Time provides us with a measure of change by :

• Putting dates on moments. e.g. "On July 20, 1969, Neil Armstrong made history by becoming the first man to walk on the moon". To talk about any moment in the past, present, and future we need to refer to the date(day, month, and year)

• Fixing the durations of events. e.g. "I studied today for 2 hours". Here the hours help me to determine how long I studied.

• Order in which events occur. e.g. "Sam reached office at 8 AM, had lunch at 1 PM, and left the office at 6 PM." Here the time attached to each event helps us to understand in what order the event occurred in a day.

To do that, some method of time measurement is needed. We use two kinds of time measurement tools:

• Clock and Watches to measure hours, minutes, and seconds. It measures the time of an event happening in a day
• A calendar is used to measure a more extended period of time( i.e. longer than a day). It measures time in days, weeks, months, and years.

Both methods are used together to specify when in time a particular event occurs (e.g. 12:30 PM on 16 December 2019).

No matter what tool we use to measure the time the unit that we use as a reference is a day. Regarding a day, there are units of time that are smaller than a day, and there are other units of time that are greater than a day. The following units are used to measure time:

Units Smaller than the Day:

• A day has 24 hours.
• One hour has 60 minutes.
• A minute has 60 seconds.

Units Larger than the Day:

• 7 days make a Week.
• A Month has 28 to 31 Days.
• A Year has 365 or 366 Days. 
• 12 Months make a Year.
• 10 Years make a Decade.
• 100 Years make a Century.

Clock is used to measure units smaller than the Day

A clock is a device used to divide a day into smaller intervals. It displays the time in hours, minutes, and often seconds, during a 12 or 24-hour period. The most common type of clocks that we use today is analog and digital clocks. The analog clock has little pointers that spin and are called a hand. The small hand tells what the hour is and the big hand tells how many minutes have passed after the hour. Along the edge of the clock, we have numbers from 1 to 12 that determine the time. The digital clock shows the time using numbers, not hands. 

A calendar is used to measure units larger than the Day

The Calendar is a table that shows days and months in a year. It will help us to relate an event with a day, month, and year.

Even before such methods were devised, mankind has always used more informal methods for basic timekeeping, such as the cycle of the seasons, and of day and night, and the position of the Sun in the sky. Sundials, water clocks, Sand clocks, and burning candle clocks are some of the time measurement tools our ancestors used.
                
Ancient peoples used the apparent motion of the Sun, the Moon, the planets, and the stars through the sky to determine the seasons, the length of the month, and the length of the year. Many early civilizations developed calendars independently.

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Refer to the lesson 'clock' and 'calendar' to learn how to measure time using them. Here are some examples to understand how to convert the units of time into seconds, minutes, hours, days, months, and years.

Example 1: Convert 7 days 2 hours into hours.
Solution: As 1 Day = 24 Hours, therefore 7 days = 7 × 24 hours = 168 hours
Total Hours = 168 hours + 2 hours =  170 hours

Example 2:  Convert 4 hours into minutes.
Solution: As 1 Hours = 60 Minutes, therefore 4 hours = 4 × 60 = 240 minutes.

Example 3: How many minutes is 360 seconds?
Solution: As 1 Minute = 60 Seconds , therefore 360 seconds = \(^{360}/_{60}\) = 6 minutes

Example 4: How many days are there in 3 weeks?
Solution: As 1 week = 7 days, therefore 3 weeks = 3 × 7 = 21 days