Physical Quantities 9th Physics

 PHYSICAL QUANTITIES

Physical Quantities are those which can be measured and have a unit are called Physical Quantities.

They are classified into two types.

1. Fundamental Quantities

2. Derived Quantities

1. Fundamental Quantities

Those quantities which are basic in nature and can not be derived from any other quantity are known as Fundamental Quantities.

For Example: Mass, Length, Time etc.

The units of fundamental quantities are called Fundamental Units.

For example: We have unit of length is Meter.

Here Length is fundamental Quantity and Meter is its fundamental Unit.

2. Derived Quantities:

Those which quantities which are derived from other fundamental quantities are termed as Derived Units.

The Units of Derived Quantities are called Derived Units.

For Example:

Force, Momentum, Density, Volume etc.

Their units are called derived units.

Before 1960, there were three systems of units they are;

1.CGS

2.MKS

3.FPS

In each system there were different units of those fundamental quantities.

In CGS which stands for Centimeter Gram Second.

In this system the units of the fundamental quantities are:

Fundamental Quantity                Units

Mass                                                        Gram

Length                                                    Centimeter

Time                                                        Second

MKS stands for Meter, Kilogram, Second, the units of fundamental quantities in this system are;

Fundamental Quantities                Units

Mass                                                            Kilogram 

Length                                                        Meter

Time                                                           Second

FPS stands for Foot, Pound Second.

In this system the units of fundamental quantities are:

Fundamental Quantity                    Units

Mass                                                               Pound

Length                                                            Foot 

Time                                                              Second

After 1960,  seven fundamental quantities were introduced and they possess standard units which are followed across the world.

These quantities are;

Fundamental Quantities                    Units

Mass                                                                Kilogram (kg)

Length                                                             Meter (m)

Time                                                                Second (s)

Electric Current                                                ampere (A)

Temperature                                                     Kelvin (k)

Amount of Substance                                       Mole (mol.)

Luminous Intensity                                           Candela (Cd)