More Articles
 Unit And Dimension
 Motion & Friction
 Work, Energy and Power
 Gravitation
 Pressure
 Floatation
 Surface Tension
 Viscosity
 Elasticity
 Simple Harmonic Motion
 Wave
 Sound Wave
 Heat
 Light
 Static Electricity
 Current Electricity
 Magnetism
 Atomic & Nuclear Physics
 Electronics
 Scientific Instruments & Thier Uses
 Inventions & their Inventors
 Important Discoveries in Physics
 S.I. Units of Physical Quantity
 Conversion of Units from One System to another System
Unit and Dimension
Unit:
The chosen standard used for measuring a physical quantity is called unit.
The unit should be:
1. Well defined
2. Easy to reproduce
3. Easy to compare
4. Internationally accepted independent of changes in physical conditions
Units are of two types:
1. Fundamental Unit and
2. Derived Unit
System of Units:
Units depend on choice. Each choice of units leads to a new system (set) of units. The internationally accepted systems are: 1. CGS system 2. MKS System 3. FPS System 4. SI Units.
In SI Units, there are seven fundamental units given in the following table:
Physical Quantity 
SI Unit 
Symbol 
Length 
metre 
m 
Mass 
kilogram 
kg 
Time 
second 
s 
Electric Current 
ampere 
A 
Temperature 
kelvin 
K 
Luminous intensity 
candela 
1 cd 
Amount of substance 
mole 
mo! 
Besides these seven fundamental units, two supplementary units are also defined, viz., radian [rad] for plane angle and steradian (sr) for solid angle.
 All the units which are defined / expressed in terms of fundamental units are called derived units.
Some important derived units
S. 
Physical Quantity 
Cgs units 
SI unit 
Relation 
1. 
Force 
Dyne 
Newton 
1 newton = 10^{5} dyne 
2. 
Work 
Erg 
Joule 
1 joule = 10^{7} erg 
Some practical units of length mass and time
Length 
Light year = distance traveled by light in one year vacuum. 1LY = 9.46 x 10^{15}m 1 Astronomical Unit (A.U.) = 1.5 x 10^{11} m 1 Parsec = 3.26 ly = 3.08 x 10^{16} m 1 Nautical mile or Seamile = 6076 ft = 1852 m 1 Micron = 1 1 Angstron (A) = 10~^{10} m 
Mass 
1 Quintal = 10^{2} kg 1 Metric ton = 10^{3 }kg 1 Atomic Mass Unit (amu) or Dalton = 1.66 x 10^{27} kg 1 Slug = 14.59 kg 1 Pound = 0.4537 kg 1 Chandrashekhar limit = 1.4 times the mass of sun = 2.8 x 10^{30} kg 
Time 
1 Solar day = 86400 sec. 1 Year = 365 ^{1/2} solar days 1 Lunar month = 27.3 solar days. Tropical year = It is the year in which total solar eclipse occurs. Leap year = It is the year in which the month of February is of 29 days. 
 Astronomical distances are measured in light year because speed of light is always the same.
Prefixes used in metric system
Prefix 
Symbol 
Multiplier 
deci 
d 

centi 
c 

milli 
m 

micro 
μ 

nano 
n 

pico 
P 

femto 
f 

atto 
a 

zepto 
z 

yocto 
y 

deca 
da 

hecto 
h 

kilo 
k 

mega 
M 

giga 
G 

tera 
T 

peta 
P 

exa 
E 

zetta 
Z 

yotta 
Y 
Dimension
Dimension of a physical quantity are the powers through which different fundamental quantities are raised to define the quantity.
The expression by which a physical quantity is defined in terms of fundamental quantities is called dimensional, formula of the quantity.
For example: Dimensional formula of momentum is MLT^{1}
S. 
Quantity 
Dimensional Formula 
1 
Volume 

2 
Density 

3 
Velocity 

4 
Acceleration 

5 
Angular Velocity, Frequency 

6 
Momentum, Impulse 

7 
Force 

8 
Work, Energy 

9 
Power 

10 
Pressure, Streess, Modulus of Elasticity 

11 
Moment of Inertia 

12 
Torque/Moment of Force 

13 
Angular Momentum, Planck’s Constent 

14 
Coefficient of Viscosity 

15 
Surface Tension 

16 
Universal Gravitational Constant 

17 
Latent Heat 

18 
Specific Heat 
More Related Articles
Motion When an object shifts its position in relation to a reference point within a specific time frame, it is said to be motion. The change in a body's position with respect to a frame of
Work If a body gets displaced when a force acts on it, work is said to be done. Work is measured by the product of force and displacement of the body along the direction of force. If a body gets
Gravitation: Every body attracts other body by a force called force of gravitation. Newton's law of Gravitation: The force of gravitational attraction between two point bodies is directly
Pressure is defined as force acting normally on unit area of the surface. SI unit of pressure is N/m2 also called pascal (Pa), Pressure is a scalar quantity. Some application of the co
Buoyant Force: When a body is immersed party or wholly in a liquid, a force acts on the body by the liquid in the upward direction. This force is called Buoyant force or force of buoyancy or upthr
Cohesive Force: The force of attraction between the molecules of same substance is called cohesive force. Cohesive force is maximum in solids. This is why solids have a fixed shape. Cohesive force is
Viscous force: The force which opposes the relative motion between different layers of liquid or gases is called viscous force. Viscosity: Viscosity is the property of a liquid by virtue of
Elasticity: Elasticity is the property of material of a body by virtue of which the body acquires its original shape and size after the removal of deforming force. Elastic Limit: Elastic limi
Periodic Motion: Any motion which repeats itself after regular interval of time is called periodic or harmonic motion. Motion of hands of a clock, motion of earth around the sun, motion of the need
A wave is a disturbance which propagates energy from one place to the other without the transport of matter. Waves are broadly of two types: 1. Mechanical Wave 2. Nonmechanical Wave 1. Me