What is the Fundamental and Derived Units in Easy words 2023

1. Fundamental and Derived Units :-

Units are of two types :-
(i) Fundamental units
(ii) Derived units.

(i) Fundamental units

The units selected for measuring the fundamental quantities ( mass , length and time) fundamental units. A fundamental unit is independent of any other unit.
All the physical quantities can be expressed in terms of these fundamental units. For measuring mass, length and time, there are independent units such as kilogram (kg), meter (m) and second (s). Hence kilogram (kg), meter (m) and second (s) are called fundamental units.
Measurement of mass, length and time is independent and cannot be resolved into any other units, hence units of mass, length and time are fundamental units.

Mass : Mass of a body is the quantity of matter contained in the body. It is an essential property of material body and hence, can never be zero. It is also not affected by the presence of other bodies near the body.

Unit of Mass : The internationally accepted unit of mass is kilogram (kg).
The general conference of weight and measures defined kilogram as the mass Of Platinum cylinder kept at the International Bureau of Weight and Measures at Sevres near Paris , France.

Length : Length of an object may be defined as the distance of separation between its two ends.

Unit of Length : Internationally accepted unit of length is meter (m). General Conference Of Weight and Measures defined meter as the distance between two lines marked as a Platinum rod kept at a constant temperature of 273•16 K at International Bureau of Weight and Measures at Sevres near Paris, France.

Time : According to Einstein, time is simply what a clock reads.

Unit of Time : Internationally accepted unit of time is second (s). Internationally accepted definition of second is given below • A second or better called a solar second is 1/24 X60 X60th or 1/86400th part a mean solar day .

Solar day is defined as the time that elapses between noons of two consecutive days and mean solar day is the average of the solar days in a complete one year.

(ii) Derived units :-

The unit of all physical quantifies can be expressed in terms of fundamental units are called derived units.
In other words. the units of derived physical quantities are called derived units because they are derived from fundamental units.
For example.
Area = Length x Length = ( Length )2 =m2
Speed = Distance / Time = m s-1
Acceleration = Velocity / Time = Length / Time2
Force = Mass x Acceleration = Mass x Length
Thus, the units of area, velocity, acceleration and force are derived from the fundamental units of mass, length and time and are therefore called derived units.

• 1.1.3. Systems of Fundamental Units :-

For the measurement of physical quantities, the following systems of fundamental units are commonly used :-
( i ) FPS System. In this system of units, the unit of length is foot, the unit of mass is pound and the unit of time is second. This system is not a metric system and was also known as British system of units. A few of units from this system are still in day-to-day use but for scientific and
research work. this system of units is not preferred. The foot is one-third of the distance between two lines on a platinum—irridium alloy bar at
a temperature of 62 OF kept at the standard office of the Board of Trade (B.O.T.), London. The pound is the mass of a platinum—irridium cylinder kept at the standard office of B.O.T. , London.
The second is defined as 1186400th part of a mean solar day. I foot = 12 inch = 12 x 2-54 = 30-48 cm
I pound = 453 g = 0453 kg

2 . CGS System. In this system of units, the unit of length is centimeter, the unit Of mass is gram and the unit of time is second. This system is a metric system of units.

The centimeter is one—hundredth part of a meter.
The gram is one-thousandth part of a kilogram.
The second is defined as 1186400th part of a mean solar day.

3 . MKS System. In this system of units, the unit of length is meter, the unit of mass is kilogram and the unit of time is second.
This system is a metric system and was first time introduced in 1901 by A. Giorgi, this system with some modifications formed the basis of SI units, which is now used in all the scientific work.