1. WHAT IS PHYSICS?
“Physics is a fundamental science concerned with understanding the natural phenomena
that occurs in our universe”.
Natural phenomena such as flow of water, heating of objects, sound of waterfall, rainbow,
thunderbolt, energy coming from nucleus … etc., which are very exciting to us and a number of
events taking place around us which are very useful in our life. All events in nature take place
according to some basic laws and revealing these laws of nature from the observed events is
physics.
“The scientist does not study physics because it is useful; he studies it
because he delights in it, and he delights in it because it is beautiful. If nature
were not beautiful, it would not be worth knowing, and if nature were not
worth knowing, life would not be worth living”
Henri Poincare
The main objective of physics is to use the limited number of fundamental laws that
governs natural phenomena to develop theories that can predict the results of future experiments.
The fundamental laws used in developing theories are expressed in the language of
mathematics, the tool that provides a bridge between theory and experiments.
Between 1600 and 1900, three broad areas were developed, which is together called
classical physics.
(i) Classical Mechanics deals with the study of the motion of particles and fluids.
(ii) Thermodynamics deals with the study of temperature, heat transfer and properties of
aggregations of many particles.
(iii) Electromagnetism deals with electricity, magnetism, electromagnetic wave, and
optics.
These three areas explain all the physical phenomena with which we are familiar.
But by 1905 it became apparent that classical ideas failed to explain several phenomena.
Then some new theories were developed in what is called Modern Physics.
Three important theories in modern physics are
(i) Special Relativity: A theory of the behavior of particles moving at high speeds. It led to
a radical revision of our ideas of space, time and energy.
(ii) Quantum Mechanics: A theory dealing with the behavior of particles at the
submicroscopic level as well as the macroscopic world.
(iii) General Relativity: A theory that relates the force of gravity to the geometrical
properties of space.
It is also useful in the study of other subjects like biotechnology, geophysics, geology etc.
,SCOPES AND EXCITEMENT
The scope of physics is very wide. We can understand the scope of physics by looking at
its various sub-discipline. It covers a very wide variety of natural phenomena. It deals with the
phenomena from microscopic level to macroscopic level. The microscopic domain includes atomic,
molecular and nuclear phenomena. The macroscopic domain includes phenomena at laboratory,
terrestrial and astronomical scales.
For example forces we encounter in nature are nuclear forces, chemical forces and forces
exerted by ropes, springs, fluids, electric charges, magnets, the earth and the Sun. Their ranges
and relative strength can be summarized as shown below in the table.
Forces Relative Range
Strength
Strong 1 10-15 m
Electromagnetic 10-2 Infinite10–
Weak 10–6 17 m
Gravitational 10-38 Infinite
Similarly the range of distance we study in physics vary from 10-14 m (size of nucleus) to
+25
10 m (size of universe)
The range of masses includes in study of physics varies from 10-30 kg (mass of electron) to
55
10 kg (mass of universe)
The range of time interval varies from 10-22 sec (time taken by a light to cross a nuclear
distance) to 1018 sec. (life time of sun).
So we can say scope of physics is really wide.
The study of physics is very exciting in many ways.
Excitement of Physics can be seen in every field.
Advancement of technology has upgraded the entire scenario of entertainment,
starting from a radio to the most advanced cyber park.
Communication system has been also deepened its root by bridging distant areas
closer.
Advances in health science, which has enabled operations without surgery.
Telescopes & satellite have broken the limits of knowledge of the undiscovered
universe.
Exploring the sources of energy from the unexplored sources.
Made possible the reach of man beyond the earth, towards the cosmos.
Use of Robots in a hazardous places is highly beneficial.
, 2. PHYSICAL QUANTITIES
All the quantities by means of which we describe the laws of nature and which can be
measured are called physical quantities. Examples are Mass, length, time, force, velocity,
acceleration etc.
‗Beauty and intelligence‘ are not physical quantities, because they can‘t be measured.
All the physical quantities have been classified into two parts
Physical Quantities
Fundamental Derived
2.1 FUNDAMENTAL PHYSICAL QUANTITY
It is an elementary physical quantity, which doesn‘t require any other physical quantity to
express it. It means it cannot be resolved further in terms of any other physical quantity. It is also
known as basic physical quantity.
In mechanics length, mass and time are only three basic physical quantities. Other basic
physical quantities are electric current, temperature, luminous intensity and amount of substance.
2.2. DERIVED PHYSICAL QUANTITY
All those physical quantities, which can be derived from the combination of two or more
fundamental quantities or can be expressed in terms of basic physical quantities, are called
derived physical quantities.
Examples: Velocity, density, force, energy etc.
Velocity can be expressed in terms of distance and time
Displacement
Velocity
Time
Density can be expressed in terms of mass and length
Mass Mass
Density
Volume (Length)3
, 3. UNITS
We know that the results of physics are based on experimental observation and
quantitative measurement, so it is also known as quantitative science.
Now to express the magnitude of any physical quantity we need a unit.
Suppose we say that the distance between two stations A and B is 500. Without a unit, we
are unable to understand how far B is from A.
But when we say that distance is 500 m or 500 km then we get a picture of how far B is
from A, since we know the standard length of meter. Similarly, when we say that the speed of an
automobile is 20, unless we also specify the units meter per second or kilometer per hour it is
meaningless. When we want to know the amount of fuel needed for a long trip it is difficult to arrive
at an answer without knowing the unit of speed.
So we can say that all physical quantity needs a unit.
The need of unit felt long-long ago in A.D. 1120. The king of England decided the unit of
length, which was yard. The yard was the distance from the tip of his nose to the end of
outstretched arm.
Similarly, the original standard for the foot adopted by the French was the length of royal
foot of king Louis XIV. This standard prevailed until 1799, until the legal standard in France
became the meter.
In this way we see that different standards were decided in different periods of time and in
different parts of the world. Due to this reason again a major problem was faced which can be
understood from this example. Suppose a visitor from another place is talking about a length of 8
―glitches‖ and we don‘t know the meaning of the unit glitch. So this talk is meaningless for us. Then
the need of a standard unit was felt which should be universal.
In 1960, an international committee was established to set a standard of unit for physical
quantities. This system is called International System (SI) of units.
3.1 UNITS
To measure a physical quantity we require a standard of that physical quantity. This
standard is called unit of that physical quantity. It can be defined in this way.
―Measurement of any physical quantity involves comparison with a certain basic
internationally accepted reference standard called unit.
Measure of physical quantity = Numerical value × Unit
Length of a rod = 8 m
where 8 is numerical value and m (metre) is unit of length.
3.2 FUNDAMENTAL AND DERIVED UNITS
There are a large number of physical quantities and every quantity needs a unit.
However, all the quantities are not independent. For example, if a unit of length is defined,
a unit of area or volume is automatically obtained. Thus, we can define a set of fundamental
quantities and all other physical quantities, which can be expressed in terms of fundamental
quantities, are derived quantities.
Fundamental Units: The units of fundamental physical quantities are called fundamental
“Physics is a fundamental science concerned with understanding the natural phenomena
that occurs in our universe”.
Natural phenomena such as flow of water, heating of objects, sound of waterfall, rainbow,
thunderbolt, energy coming from nucleus … etc., which are very exciting to us and a number of
events taking place around us which are very useful in our life. All events in nature take place
according to some basic laws and revealing these laws of nature from the observed events is
physics.
“The scientist does not study physics because it is useful; he studies it
because he delights in it, and he delights in it because it is beautiful. If nature
were not beautiful, it would not be worth knowing, and if nature were not
worth knowing, life would not be worth living”
Henri Poincare
The main objective of physics is to use the limited number of fundamental laws that
governs natural phenomena to develop theories that can predict the results of future experiments.
The fundamental laws used in developing theories are expressed in the language of
mathematics, the tool that provides a bridge between theory and experiments.
Between 1600 and 1900, three broad areas were developed, which is together called
classical physics.
(i) Classical Mechanics deals with the study of the motion of particles and fluids.
(ii) Thermodynamics deals with the study of temperature, heat transfer and properties of
aggregations of many particles.
(iii) Electromagnetism deals with electricity, magnetism, electromagnetic wave, and
optics.
These three areas explain all the physical phenomena with which we are familiar.
But by 1905 it became apparent that classical ideas failed to explain several phenomena.
Then some new theories were developed in what is called Modern Physics.
Three important theories in modern physics are
(i) Special Relativity: A theory of the behavior of particles moving at high speeds. It led to
a radical revision of our ideas of space, time and energy.
(ii) Quantum Mechanics: A theory dealing with the behavior of particles at the
submicroscopic level as well as the macroscopic world.
(iii) General Relativity: A theory that relates the force of gravity to the geometrical
properties of space.
It is also useful in the study of other subjects like biotechnology, geophysics, geology etc.
,SCOPES AND EXCITEMENT
The scope of physics is very wide. We can understand the scope of physics by looking at
its various sub-discipline. It covers a very wide variety of natural phenomena. It deals with the
phenomena from microscopic level to macroscopic level. The microscopic domain includes atomic,
molecular and nuclear phenomena. The macroscopic domain includes phenomena at laboratory,
terrestrial and astronomical scales.
For example forces we encounter in nature are nuclear forces, chemical forces and forces
exerted by ropes, springs, fluids, electric charges, magnets, the earth and the Sun. Their ranges
and relative strength can be summarized as shown below in the table.
Forces Relative Range
Strength
Strong 1 10-15 m
Electromagnetic 10-2 Infinite10–
Weak 10–6 17 m
Gravitational 10-38 Infinite
Similarly the range of distance we study in physics vary from 10-14 m (size of nucleus) to
+25
10 m (size of universe)
The range of masses includes in study of physics varies from 10-30 kg (mass of electron) to
55
10 kg (mass of universe)
The range of time interval varies from 10-22 sec (time taken by a light to cross a nuclear
distance) to 1018 sec. (life time of sun).
So we can say scope of physics is really wide.
The study of physics is very exciting in many ways.
Excitement of Physics can be seen in every field.
Advancement of technology has upgraded the entire scenario of entertainment,
starting from a radio to the most advanced cyber park.
Communication system has been also deepened its root by bridging distant areas
closer.
Advances in health science, which has enabled operations without surgery.
Telescopes & satellite have broken the limits of knowledge of the undiscovered
universe.
Exploring the sources of energy from the unexplored sources.
Made possible the reach of man beyond the earth, towards the cosmos.
Use of Robots in a hazardous places is highly beneficial.
, 2. PHYSICAL QUANTITIES
All the quantities by means of which we describe the laws of nature and which can be
measured are called physical quantities. Examples are Mass, length, time, force, velocity,
acceleration etc.
‗Beauty and intelligence‘ are not physical quantities, because they can‘t be measured.
All the physical quantities have been classified into two parts
Physical Quantities
Fundamental Derived
2.1 FUNDAMENTAL PHYSICAL QUANTITY
It is an elementary physical quantity, which doesn‘t require any other physical quantity to
express it. It means it cannot be resolved further in terms of any other physical quantity. It is also
known as basic physical quantity.
In mechanics length, mass and time are only three basic physical quantities. Other basic
physical quantities are electric current, temperature, luminous intensity and amount of substance.
2.2. DERIVED PHYSICAL QUANTITY
All those physical quantities, which can be derived from the combination of two or more
fundamental quantities or can be expressed in terms of basic physical quantities, are called
derived physical quantities.
Examples: Velocity, density, force, energy etc.
Velocity can be expressed in terms of distance and time
Displacement
Velocity
Time
Density can be expressed in terms of mass and length
Mass Mass
Density
Volume (Length)3
, 3. UNITS
We know that the results of physics are based on experimental observation and
quantitative measurement, so it is also known as quantitative science.
Now to express the magnitude of any physical quantity we need a unit.
Suppose we say that the distance between two stations A and B is 500. Without a unit, we
are unable to understand how far B is from A.
But when we say that distance is 500 m or 500 km then we get a picture of how far B is
from A, since we know the standard length of meter. Similarly, when we say that the speed of an
automobile is 20, unless we also specify the units meter per second or kilometer per hour it is
meaningless. When we want to know the amount of fuel needed for a long trip it is difficult to arrive
at an answer without knowing the unit of speed.
So we can say that all physical quantity needs a unit.
The need of unit felt long-long ago in A.D. 1120. The king of England decided the unit of
length, which was yard. The yard was the distance from the tip of his nose to the end of
outstretched arm.
Similarly, the original standard for the foot adopted by the French was the length of royal
foot of king Louis XIV. This standard prevailed until 1799, until the legal standard in France
became the meter.
In this way we see that different standards were decided in different periods of time and in
different parts of the world. Due to this reason again a major problem was faced which can be
understood from this example. Suppose a visitor from another place is talking about a length of 8
―glitches‖ and we don‘t know the meaning of the unit glitch. So this talk is meaningless for us. Then
the need of a standard unit was felt which should be universal.
In 1960, an international committee was established to set a standard of unit for physical
quantities. This system is called International System (SI) of units.
3.1 UNITS
To measure a physical quantity we require a standard of that physical quantity. This
standard is called unit of that physical quantity. It can be defined in this way.
―Measurement of any physical quantity involves comparison with a certain basic
internationally accepted reference standard called unit.
Measure of physical quantity = Numerical value × Unit
Length of a rod = 8 m
where 8 is numerical value and m (metre) is unit of length.
3.2 FUNDAMENTAL AND DERIVED UNITS
There are a large number of physical quantities and every quantity needs a unit.
However, all the quantities are not independent. For example, if a unit of length is defined,
a unit of area or volume is automatically obtained. Thus, we can define a set of fundamental
quantities and all other physical quantities, which can be expressed in terms of fundamental
quantities, are derived quantities.
Fundamental Units: The units of fundamental physical quantities are called fundamental
