`color{blue} ☞` Physics is a branch of science. The word ` 'Physics'` has come from a Greek word meaning nature. The word `'Science' ` has come from a Latin word 'Scientia' which means 'to know'. Thus, Physics is the subject of studying nature and natural phenomena.


` color{blue} ☞ color{blue} ul("Science")`

Man has always been curious about the natural phenomena taking place around him, such as, daily repetition of sunrise and sunset, yearly repetition of seasons, regular motion of the moon and other heavenly objects in the sky, etc. He has responded to these phenomena in a systematic manner. The knowledge thus gained which has been transferred from generation to generation, each generation adding new facts to it, is known as 'Science'.

`color{purple}(✓✓)color{purple} " DEFINITION ALERT"`

`color{blue} ☞color{blue} ul(mathtt ("Science"))` is the study of the nature and behaviour of natural things and the knowledge that we obtain about them.

The knowledge of science is acquired through a method consisting of the following four steps:
(i) observation of facts
(ii) proposing theory or hypothesis to explain the observation
(iii) testing the validity of the theoretical predictions based on the proposed theory
(iv) modification of the theory, if necessary.

` color{blue}☞color{blue} ul("Hypothesis")`
A hypothesis is a supposition without assuming that it is true. It would not be fair to ask anybody to prove the universal law of gravitation, because it cannot be proved. It can be verified and substantiated by experiments and observations.

` color{blue}☞color{blue} ul("Axiom")`
An axiom is a self-evident truth.

` color{blue}☞color{blue} ul("Model")`
A model is a theory proposed to explain observed phenomena.

The technology is the practical application of Physics and other branches of science which has played important role in the development of various industries and in raising the standard of living of the society. Some applications of Physics are as follows :

• The Newton's laws of motion find application in the flight of rockets, and Bernoulli's theorem in the designing of aeroplane wings.

• The principles of thermodynamics have been utilized in heat engines (steam, petrol and diesel) and in refrigerators and air-conditioners.

• The electric bulbs, lamps and tubes are based on conversion of electric energy into light.

•The electromagnetic induction, discovered by Faraday, has found application in electric generators, motors, furnaces, etc.

• Some other applications are hydroelectric power stations generating electricity, thermal power stations, nuclear reactors, radio, television and wireless communication, calculators and computers etc.

Thus, Physics plays an important role in technology and in our daily lives.

The developments in Physics are having a direct impact on Society. A number of examples can be given :

• Telephone, telegraph, telex, teleprinter and now fax are extensively used by housewives, businessman industrialists and professionals.

• Radio, television and satellites, as means of communication, have connected all parts of the world together.

• Calculators, computers and lasers have changed the day-to-day life of the mankind.

• Exploration of the new sources of energy has become absolutely necessary for the existence of future generation.

• The development of nuclear power has become a threat to the existence of life on earth.

` color{blue} ☞color{blue} ul("Gravitational Force")`
The forces of attraction existing between any two separated bodies due to their masses are called gravitational forces.

` color{blue}☞color{blue} ul("Weak Nuclear Force")`
The weak nuclear force appears only in certain nuclear processes such as the β-decay of a nucleus.
The weak nuclear forces are the forces which cause light elementary particles to interact with one another and with heavier particles.

` color{blue} ☞color{blue} ul("Strong Nuclear Force")`
These forces are nuclear origin. They are responsible for holding neutrons and protons together inside atomic nucleus.

` color{blue} ☞color{blue} ul("Electromagnetic Force")`
Electromagnetic force is the force between charged particles. In the simpler case when charges are at rest, the force is given by Coulomb’s law : attractive for unlike charges and repulsive for like charges. Charges in motion produce magnetic effects and a magnetic field gives rise to a force on a moving charge. Electric and magnetic effects are, in general, inseparable – hence the name electromagnetic force.

Physicists explore the universe. Their investigations range from particles smaller in size than atoms to extremely distant stars. Besides finding facts about nature by observation and experimentation, physicists try to discover the laws that govern these facts.

In any physical phenomenon taking place in nature, several quantities change with time, while some special physical quantities remain constant in time. The later quantities are 'conserved quantities' of nature, and are governed by certain conservation laws. Some of the general conservation laws in nature are the following :

• Conservative of Mechanical Energy
• Conservative of Total Energy of an Isolated System
• Conservative of Mass plus Energy
• Conservative of Momentum
• Conservative of Charge
• Conservative of the Number of Nucleons (Mass Number)