Physical Quantities and Measuring|9thClass ChapterNo1(part 1)|tutoronlines

Chapter 1

Physical Quantities and Measuring

Major Concepts

1.1 Introduction of physics
1.2 Physical Quantities
1.3 International system units
1.4 Prefixes ( multiples and sub multiples)
1.5 Scientific notation/ Standard form
1.6 Measuring Instruments
1.6.1 Metre rules

1.6.2 Vernier calliper
1.6.3 Screw gauge
1.6.4 Physical balance
1.6.5 Stopwatch
1.6.6 Measuring cylinder
1.7 An introduction to significant figures


The knowledge gain through observation and experimentation is call Science. The world science is derived from the Latin word Scientia. Which means knowledge.

Natural Philosophy:

Not until eighteenth century, various aspect of material objects were studied under a single subject called natural Philosophy.

Physical science:

Which deals with the study or non-living things is called Physical science.

Biological Sciences:

The branch of science which deals with the study of living things is called Biological Sciences.


Physics is the branch of science that deals with matter, energy and their relationship is called Physics.

Branches of Physics


It is the study of motion of objects, its causes and effects.


It deals with the nature of heat, modes of transfer and effects of heat.


It deals with the physical aspect of sound waves, their production, properties and applications.

Light (Optics):

It is the study of physical aspect of light, it’s properties, working and use of optical instruments.

Electricity and Magnetism:

It is the study of the charges at rest and in motion, heir effect and their relationship with magnesium.

Atomic Physics:

It is the study of the structure and properties of atoms.

Nuclear Physics:

It deals with the properties and behaviour of nuclei and the particles within the nuclei.

Plasma Physics:

It is the study of production, properties of the ionic state of matter.( The fourth state of matter)


It is the study of internal structure of the Earth.

Physical Quantities:

All measurable quantities are called physical Quantities. Such as length, mass, time and temperature. A physical Quantities possesses at least two characteristics in common. One is its numerical magnitude and the other is the unit in which it is measured. Physical Quantities are divided into two types.

Types of Physical Quantities:
1- Base Quantities:

Base quantities are the quantities on the basis of which other quantities are expressed. These are length, mass, time, electric current, temperature, intensity of light and the amount of a substance.

2- Derived Quantities:

The quantities that are expressed in terms of base quantities are called derived quantities. These including area, volume, speed, force, work energy, power, electric charge, electric potential, etc.

International system of units:

Thus, there is a need of some standard quantities for measuring/comparing unknown quantities. Once a standard is set for a quantity then it can be expressed in terms of that standard quantity. This standard quantity is called a unit.

The eleventh Geranyl Conference on weight and measure help in Paris in 1960 adopted a world-wide system of measurement called International system of units. Its represent by SI.

Base unit:

The units that well be described by base quantities are called base units. See by the table.

Name Symbol Name Symbol
Length l Meter m
Mass m Kilograms kg
Time t Second S
Electric current I Ampere A
Intensity of light L Candela Cd
Temperature T Kelvin K
Amount of a substance n Mole mol
Derived units:

The units used to measure device quantities are called derived units. Speed is define as distance cover in units time therefore its units is metre per second. see by the table.


Name Symbol
speed v
Acceleration a
Volume V
Force F
Pressure P
Density P
Charge Q

Name Symbol
Metre per second ms-1
Metre per second per second ms-2
Cubic metre m3
Newton N or ( kgms-2)
Pascal Pa or (Nm-2)
Kilograms per cubic metre kgm-3
coulomb C or (As)


SI units have the advantage that their multiples and sub-multiples can be expressed in terms of prefixes. Prefixes are the words or letter added before SI units such as kilo, mega, giga and milli. see by the table.

Prefix Symbol Multiplier
Exa E 1018
Peta P 1015
Tera T 1012
Giga G 109
Mega M 106
Kilo K 103
Hecto h 102
Deca da 10
Deci d 10-1
Centi C 10-2
Milli m 10-3
Micro U 10-6
Nano n 10-9
Pico P 10-12
femto F 10-15
atto a 10-18

Table of multiples and sub multiples of the length

1km 103m
1cm 10-2m
1mm 10-3m
1um 10-6m
1nm 10-9m

Scientific Notation:

In Scientific notation a number is expressed as some power of ten multiplied by a number between 1 and 10.

Scientific Notation is means that the number is expressed in  some power form. The power is ten multiplied by a number so it is placed in decimal form. A simple but scientific way to write large or small number is to express them in some power of ten. The moon distance away from the earth is 384000000 metres. The distance of the moon from the earth can also be written in the form 3.84 x 108 m. This form of expressing a number is called the standard form or scientific notation.  


A number 62740 can be expressed as 6.274 x 104 or 62.740 x 103 or 0.6274 x 105

All of these are correct. No one is incorrect. But the number that has one non-zero digit before the decimal.

Measuring instruments:

measuring instrument are used to measure various physical quantities such as length, mass, time, volume, etc.

The metre rule:

A metre rule is a length measuring instrument. It is commonly used in laboratories to measuring the length of the object or distance between two points. One milli metre is the smallest reading that can be taken using a metre rule and is called its least count.

While measuring the length, or distance, eyes must be kept vertically above the reading point. The reading of the metre rule is doubtful if the eyes is positioned either left or right to the reading point.

The Measuring Tape:

Measuring tape are used to measure the length in meter or centimetres. A measuring tapes are used by black smith and carpenters. A measuring tape is contain a thin and large strip of cotton, metal, or plastic generally 10m, 20m, 30m, 40, 50, or 100m long. Measuring tape are marked in present a centimetres as well as in inches.

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