Measurement


Measurement:- Measurement is defined as the process of comparison of an unknown quantity with a known or standard quantity.

In ancient times there are no standard measurements like inches, centimetres, grams, feet etc. In that time hey used cubits, spans etc. One person's cubit or span is different from others. Sometimes the quarrels also happened. So some people discussed and invented three different systems of measurement. They are CGS System, FPS System and MKS Systems.

Ancient systems of measurement with units
Measuremnt CGS FPS MKS
Length centimetre(cm) foot(ft) metre(m)
Mass gram(g) pound(#) kilogram(kg)
Time second(s) second(s) second(s)



Mindmapping


With these systems also some problems came. In one place one person used one system. In another place other system was used. With that when people of one place shifted to another place they don't know that measurement. So they used their place system only. The measuremnet is different now. So the quarrel came with these systems also. So they again discussed and invented one common system that is known as S.I system(Standard International system).

S.I system

In this S.I system the measurement is divided into two. They are physical quantities and non-physical quantities.
1.Physical quantities:- Quantities which can be measured physically are called physical quantities.
Examples :- Length, Mass, Time etc..,

2.Non-physical quantities:- Quantities which can't be measured physically are called non-physical quantities.
Examples:- Happiness, Sadness, Color, Taste etc..,


Again the physical quantities are divided into three. They are fundamental physical quantities, supplementary physical quantities, derived physical quantities.

1.Fundamental physical quantities:- Quantities which do not depend on other physical quantities are called fundamental physical quantities>
There are seven fundamental physical quantities. They are:- 1.Length, 2.Mass, 3.Time, 4.Thermodynamic temperature, 5.Electric current, 6.Luminous Intensity, 7.Amout of substance.

Fundamental physical quantities with units
Fundamental physical quantity Unit Symbol
Length metre m
Mass kilogram kg
Time second s
Thermodynamic temperature kelvin K
Electric current ampere A
Luminous Intensity candela Cd
Amount of substance mole mol


Supplementary physical quanitites:- Supplementary physical quantity is a physical quantity that is used for calculation (on a secondary level). Plane angle and solid angle are two supplementary units of two purely" geometrical physical quantities.

Supplementary physical quantities with units
Supplementary physical quantity Unit Symbol
Plane angle radian rad
Solid angle steradian sr


Derived physical quantities:- Quantitites which depend on other physical quantities are called derived physical quantities.
Examples:- Speed, Velocity, Density,Area, Volume etc.


Mindmapping


Fundamental units:- Units of fundamental physical quantities are called fundamental physical quantities.
Examples:- kilogram, ampere, second, metre etc.

Derived units:- Units of derived physical quantities are called derived physical quantities.
Examples:- m2, m3 etc.

Multiples and submultiples of units


Multiples:- Units used to measure larger quantities are caled multiples.

Submultiples:- Units used to measure smaller quantities are caled submultiples.

Example:- We can't use metre for all purposes. When we measuring distance from India to USA we can't understand in metres. So we use kilometers and when we are measuring thickness of a pencil metre is not sufficient. So we use millimetres.In these cases kilo is a multiple of metre and milli is submultiple of same unit metre.

Some important prefixes for units in S.I System

Prefix Multiple Symbol
Deca 101 da
Kilo 1000 = 103 kg
Mega 1000000 = 106 M
Giga 1000000000 = 109 G
Tera 1000000000000 = 1012 T


Prefix Submultiple Symbol
Deci 1/10th = 10-1 d
Centi 1/100th = 10-2 c
Milli 1/1000th = 10-3 m
Micro 1/1000000th = 10-6 Greek letter mu
Nano 1/1000000000th = 10-9 n
Pico 1/1000000000000th = 10-12 p


Rules for writing S.I Units
  1. The symbols used for units are always written in lowercase.
    2. S.No Quantity Correct Wrong
    1 Mass kg Kg
    2 Length m M
    3 Time s S
  2. Name of the unit should start with lowercase letter even if it is named after a scientist.
    3. S.No Quantity Correct Wrong
    1 Force newton Newton
    2 Temperature kelvin Kelvin
    3 Energy joule Joule
  3. Symbol of unit name after a scientist, should start with with an uppercase letter.
    4. S.No Quantity Correct Wrong
    1 Force N n
    2 Temperature K k
    3 Energy J j