Measurment : Class 9th Notes

Measurement

Physical quantity 

Those quantities which can be measured are called physical quantities.

Example :- velocity, acceleration, force, area, volume, pressure, distance etc.

Measurement 

Those process of comparing and unknown physical quantity with respect to a known physical quantity is known as measurement.

Measurement of any physical quantity consists of two parts.

• Numerical value

• unit

        Q = nu

        Q = measurement

        n = numerical value

        u = unit

Kinds of physical quantity

✓There are two types of physical quantity.

1. Fundamental physical quantity

2. Derived physical quantity

Fundamental physical quantity 

Those quantity which do not depend on other quantities and also independent of each other.

There are seven fundamental physical quantity.

            Length ...............metre

            Mass ...............kilogram

            Time ...............second

            Temperature ...............Kelvin

            Electric current ...............ampere

            Luminous intensity ...............candala

            Amount of substance ...............mole

Derived physical quantity

Those quantities which are derived from fundamental physical quantity.

Example :- Velocity = m/s

                    Acceleration = m/s²

Unit :- To measure of physical quantity it is compared with standard quantity this standard quantity is called unit.

Types of unit

1. Fundamental unit :- Those unit which cannot be derived from any other unit is called fundamental unit.

Example - m, sec, K etc.

2. Derived unit :- Any unit which can be obtained by the combination of one or more fundamental unit are called derived unit.

Example : m³, m/s, m/s² etc.

System of units

Depending upon the units of fundamental physical quantities, there are four main system of units.

System of unit	Length	Mass	Time
1. C.G.S	Centimeter	Gram	Second
2. F.P.S	Foot	Pound	Second
3. M.K.S	Meter	Killogram	Second
4. SI	System International of units

Characteristics of a standard unit

 • It should be a convenient size

 • It should be a very well defined

 • It should be independent of time and place

 • It should be easily available so that all laboratories can duplicate and use as per requirement.