Class 9 Science Note

Measurement

A unit is defined as a convention to define an amount of physical property in a specific system of units.

 

Fundamental unit: The units of the fundamental quantities are called fundamental unit. Those units which are independent cannot be derived from other unit is called fundamental unit.

Physical Quantity

Unit

Symbol

mass

kilogram

kg

length

meter

m

time

second

s

temperature

Kelvin

K

electric current

ampere

A

amount of matter

mole

mol

luminous intensity

candela

Cd

 

Derived units are composed of the fundamental units and are originated from the products and ratios of the fundamental units. Derived units belong to physical quantities that are derived from basic physical properties. Examples are:

Velocity – a physical quantity derived from fundamental quantities of length and time

               velocity  = distance / time  = m/s 

So the units of velocity is ms-1

 

Difference between fundamental and derived unit

Fundamental unit

Derived unit

The units of the fundamental quantities are called fundamental unit.

e.g kilogram , meter,  second  are the fundamental units

The units which are derived from the fundamental units are called derived units.

Newton, joules   are the derived units.

 


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