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Hi viewers:

Today we will discuss about the physical quantity – TIME.
It the most important physical quantity because we are consciously, sub-consciously even un-consciously we are calculating time.  In this blog we will try to give you a rough idea about time


Earth possesses two kinds of motions, one of them is rotational motion.

The rotational motion from west to east on the geographical axis is called the diurnal motion, which causes day and night.

When the sun attains the highest position in the celestial sphere, it is said to be on the meridian.

The interval of time between any two successive passage of the sun across the meridian is called an apparent solar day.

But for the same reasons, on measuring the lengths of the apparent solar day for some consecutive days, we see it is not constant but it varies slowly.

The average taken over a year is known as a mean solar day.


A mean solar day has 24 hours

1/24 th part of it is an hour

1/60 th part of an hour is a minute

1/60 th part of a minute is a second

Therefore, 1/86400 th part of a mean solar day is a second


1 decade = 10 years

1 century = 10 decades = 10 x 10 years = 100 years

1 millennium =  10 centuries


The units of time

In CGS system: second

In FPS system:  second

In MKS system:  second


Instruments for measuring time

Clock and watches

Formats of Clock

12 – hour format, which we are used to

24 – hour format, which is used in the Airports and railway stations to avoid confusions


So, What is TIME ?

Time is the interval between two events.


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Hi viewers My name is Partha Pratim Goswami, (PpG) I am a teacher by profession. I have been teaching biology, chemistry and physics, sometimes mathematics also for last sixteen years. I would like to share my entire experience with all the viewers across the world through YouTube, which I think is an amazing platform to share all my experiences.

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