It has been in the nature of man since beginning to explore the secrets of the universe. This inherent instinct of unscrambling the mysteries of the universe led him to find explanations for many such phenomena which formed the basis of philosophy. The verification of these phenomena formed the basis of science. In ancient times, Physics was called natural philosophy. Later on, when the phenomena of nature proved to be correct, philosophy was established as a branch of science called Physics. Aristotle and Archimedes were the two most famous philosophers of ancient Greece. Galileo, Newton and Einstein form the trinity of modern physicists. Year 2005 was celebrated all over the world as “The Year of Physics” to commemorate 100 years of the famous discoveries of Albert Einstein. The zeal of knowing about the big outer world and the small inner world is still going on.
The term Physics has its origin from the Greek word “Physikos” means “natural”. It is the most fundamental of all Sciences and deals with nature and natural phenomenon. It gives answers to so many questions: why there are seven colours in the rainbow? Why the clouds are in motion? Why heat from sun is essential for life on earth? Why the water in the ocean appears bluish when water is a colourless liquid? Why the aeroplane, the clouds, the cars, the birds, the hands of clock and all human beings are in motion, etc.? More specifically, Physics deals with number of physical phenomena varying from microscopic particles such as quarks (smallest unit of atom) to macroscopic bodies such as quasars (largest celestial body). A system is said to be macroscopic if it is large enough to be seen by our eyes with linear dimensions (> 10-6 m). On the other hand, microscopic systems are roughly of atomic dimensions varying from micrometre (10-6 m) to femtometre (10-15 m) and are too small to be seen even with microscopes. The occurrence of Big Bang and the origin of macroscopic things such as sun, planets, stars, galaxies as well as microscopic things such as cells (building block of life), tissues, organs and our planet earth are also based on certain laws of Physics which predicts "Physics is everywhere". It explains the existence of both macroscopic as well as microscopic things in the universe and existence of the universe itself. Concepts of position, momentum and time play an important role in our daily life. Our day begins with physics and ultimately ends with physics. We move from bed (in motion), do work, switch on lights, hear sound, use heat, use energy etc. At night, we turn off the TV, switch off the lights. Physics lays the foundation on which all the other sciences are built.
The branch of Physics which explains the motion of particles or system of particles when subjected to forces is called mechanics. Mechanics has played a significant role in the development of various disciplines of physics. Traditionally, mechanics was divided into two main branches: Statics and Dynamics. Statics is the study of objects at rest while dynamics is the study of objects in motion. Concepts of mechanics are essential for understanding the world around us and phenomena on scales from atomic to cosmic.
We live in a beautiful and complex world in which our sense ability is macroscopic. In macroscopic world, all the physical phenomena are described by classical physics or classical mechanics. The development of classical mechanics is based on well known Newton’s three laws of motion which govern the motion of objects in sufficiently large dimensions particularly the motion of planets, stars, galaxies etc. The study of motion of particles either at rest or moving at speeds less than the speed of light is called classical non relativistic mechanics. On the other hand, the study of motion of particles moving at speeds close to the speed of light is called classical relativistic mechanics. Moreover, both relativistic and non relativistic classical mechanics has limited domain. It cannot explain the microscopic or atomic phenomena such as motion of atoms, protons, electrons, neutrons and many other subatomic particles. But there also exists another world of mechanics: the world of the super tiny where Newton’s laws no longer apply. This amazing world of mechanics which explains the motion of microscopic particles is called quantum physics or quantum mechanics: fundamental theory of nature at small scales and at low energy levels of atoms and subatomic particles. In particular, it explains the motion of molecules, atoms, protons, electrons, neutrons and many other elementary particles. The work of Planck, Einstein and Bohr formed the basis for the development of quantum mechanics. Quantum mechanics has further served as a basis for the development of many other branches of physics such as atomic physics, nuclear physics, particle physics, solid state physics and finally for the understanding of the structure and origin of the world in which we live. The development of quantum physics has revolutionised our understanding of the super-tiny world and has led to discovery of fascinating behaviour which is exhibited by particles at microscopic level. This has also led to the development of new technologies such as super-computers, lasers, CDs etc. The human quest to unravel the mysteries of the universe from the super big to the super tiny and to provide explanations for these mysteries form the basis of this wondrous branch of Science called Physics.