Chapter 1
Physical World

Science is a systematic understanding of natural phenomena in detail so that it can be predicted, controlled and modified. Science involves exploring, experimenting and speculating phenomena happening around us.
The word Science originates from the Latin verb Scientia meaning ‘to know’. The Sanskrit word Vijnan and the Arabic word ilm convey similar meaning, namely ‘knowledge’. Science, in a broad sense, is as old as human species.

Scientific method is a way to gain knowledge in a systematic and in-depth way.
It involves:
 Systematic observations
 Controlled experiments
 Qualitative and Quantitative reasoning
 Mathematical modelling
 Prediction and verification (or falsification) of theories
 Speculation or Prediction

Science does not have any final theory. The improved observations, accurate tools keep improving the knowledge and perspective. Johannes Kepler used Tycho Brahe’s research on planetary motion to improve Nicolas Copernicus theory.
Quantum mechanics was developed to deal with atomic and nuclear phenomena. Work of Ernest Rutherford on nuclear model of atom became basis of quantum theory given by Niels Bohr. Antiparticle theory of Paul Dirac led to the discovery of antielectron (positron) by Carl Anderson.


Natural science is a branch of science concerned with the description, prediction, and understanding of natural phenomena, based on observational and empirical evidence.
It consists of following disciplines:
 Physics
 Chemistry
 Biology


Physics is a study of basic laws of nature and their manifestation in different natural phenomena. Physics is the study of physical world and matter and its motion through space and time, along with related concepts such as energy and force.
Word Physics is derived from a Greek word phusikḗ meaning nature. Its Sanskrit equivalent is Bhautiki that is used to refer to the study of the physical world.
We can broadly describe physics as a study of the basic laws of nature and their manifestation in different natural phenomena.

Two principal thrusts / types of approaches in physics are: Unification and Reduction.
(i) Unification:
 Attempts to explain diverse physical phenomena in terms of a few concepts and laws.
 Attempts to unify fundamental forces of nature reflects this quests.

For example, the same law of gravitation (given by Newton) describes the fall of an apple to the ground, the motion of the moon around the earth and the motion of planets around the sun. Similarly, the basic laws of electromagnetism (Maxwell’s equations) govern all electric and magnetic phenomena.
(ii) Reductionism:
Attempts to drive the properties of a bigger more complex system from the properties and interactions of its constituent simpler parts.
For example, thermodynamics was developed to explain macroscopic quantities such as temperature, internal energy etc. of the bulk system. Later on these properties were explained in terms of molecules in kinetic theory and statistical mechanic.


 It can explain a phenomena happening over a large magnitude with a simple theory.
 Experiments and observations are used to develop new theories for unidentified phenomena and improve old theories for existing phenomena.
 Development of devices using laws of physics.


Scope of Physics is vast as it covers quantities with length magnitude as high as 1040m or more (astronomical studies of universe) and as low as 10-14m or less (study of electrons, protons etc). Similarly the range of time scale goes from 10-22s to 1018s and mass from 10-30kg to 1055kg.

Physics is broadly divided into two types based on its scope – Classical Physics and Modern Physics.
Classical physics deal with the macroscopic phenomena while the Modern physics deals with the microscopic phenomena.

Macroscopic Domain
Macroscopic domain includes phenomena at large scales like laboratory, terrestrial and astronomical.
It includes following subjects:

  1. Mechanics – It is based on Newton’s laws on motion and the laws of gravitation. It is concerned with motion/equilibrium of particles, rigid and deformable bodies and general system of particles.
    a. Propulsion of rocket by ejecting gases
    b. Water/Sound waves
    c. Equilibrium of bent rod under a load
  2. Electrodynamics – It deals with electric and magnetic phenomena associated with charged and magnetic bodies.
    a. motion of a current-carrying conductor in a magnetic field
    b. the response of a circuit to an ac voltage (signal)
    c. the propagation of radio waves in the ionosphere
  3. Optics – It deals with phenomena involving light.
    a. Reflection and refraction of light
    b. Dispersion of light through a prism
    c. Colour exhibited by thin films
  4. Thermodynamics – It deals with systems in macroscopic equilibrium and changes in internal energy, temperature, entropy etc. of systems under application of external force or heat.
    a. Efficiency of heat engines
    b. Direction of physical and chemical process

Microscopic Domain
Microscopic domain includes phenomena at minuscule scales like atomic, molecular and nuclear.
It also deals with interaction of probes like electrons, photons and other elementary particles.
Quantum theory has been developed to handle these phenomena.



Physics is exciting in many ways. Application and exploitation of physical laws to make useful devices is the most interesting and exciting part and requires great ingenuity and persistence of effort.
Excitement comes from:
 Few basic concepts and laws can explain many phenomena.
 Imaginative new experiments.
 Application to make useful devices.
 Applicable in daily life.
 Prediction of future events.


 Quantitative analysis along with qualitative analysis.
 Application of universal laws in different contexts.
 Approximation approach (complex phenomena broken down into collection of basic laws).
 Extracting and focusing on essential features of a phenomenon.


 Hypothesis is a supposition without assuming that it is true. It may not be proved but can be verified through a series of experiments.
 Axiom is a self-evident truth that it is accepted without controversy or question.
 Model is a theory proposed to explain observed phenomena.
 Assumption is the basis of physics, where a number of phenomena can be explained.
These assumptions are made from experiments, observation and a lot of statistical data.


The connection between physics, technology and society can be seen in many examples.
Technology gives rise to new physics:
 The discipline of thermodynamics arose from the need to understand and improve the working of heat engines which had great impact on the course of human civilisation and triggered the industrial revolution.

Physics gives rise to new technologies:
 Silicon ‘chip’ that triggered the computer revolution in the last three decades of the twentieth century.
 Wireless communication technology that followed the discovery of the basic laws of electricity and magnetism in the nineteenth century.


Several examples where Physics and its concepts have led to discoveries/inventions are listed below.
 Steam engine was developed from the industrial revolution in eighteenth century.
 Wireless communication was developed after discovery of laws of electricity and magnetism.
 Neuron-induced fission of uranium, done by Hahn and Meitner in 1938, led to the formation of nuclear power reactors and nuclear weapons.
 Conversion of solar, wind, geothermal etc. energy into electricity.

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