0.1 What is physics?

The word physics is derived from Greek word fusis , meaning nature or natural things. As such, physics is defined as that branch of science, which studies natural phenomenain terms of basic laws and physical quantities. The study is generally structured to satisfy queries, arising from the observedevents occurring around our world. In this sense, Physics answers questions about universe and the way elements of universe interactto compose natural phenomena.

The underlying principles in physics are simple and general, but defining (basic) in nature. Elements and quantities used to describe natural phenomena are alsogeneral and basic. The whole of universe, as a matter of fact, can be considered to be comprising of two basic quantities : (i) matter and (ii) energy. For this reason, some physicists rightly define physics as the study of matter andenergy.

Domain of physics

The domain of physics extends from the infinitesimal to the infinite and is largely undefined. At one end of the scale, there are quarks composing nucleons (neutrons and protons) and on the other end, there are galaxies, with sun-like stars as its constituents and a universe that we do not know much about.

In physics, domains are also defined in terms of various important attributes like speed, temperature and other physical quantities. In the domain defined by speed, we study both stationary objects and objects moving at very high speed, perhaps three – fourths of the speed of light. It is thanks to the extraordinary efforts of scientists in the last two centuries that we now know some of the important bounds of nature. For example, the upper limit of speed is the speed of light in a vacuum. Similarly, the lower limit of temperature is 0 K. These are some of the highlights of the development of our basic understanding of nature and its extent.

The uncertainty about the domain of physics stems from the fact that new experiments and discoveries continuously break the bounds (limits) set before. An example: for many years, the charge on the electron was considered the smallest amount of charge, but today after the discovery of quarks, we know that these carry lesser amounts of charge than that carried by electrons. Thus, the extent of physics is actually changing as we learn more and more about nature.

Generality

Theories of physics are extremely general, being the underlying governing principles of natural events extending to the whole universe. This aspect contrasts physics from other streams of science, which are often specific and sometimes localized. Generality of physics and its theories render physical laws to form the basic scientific framework upon which other branches of science are developed. Take the example of charged molecules called "ions" - a subject of investigation in Chemistry. Oppositely charged ions are glued together under the influence of an electrostatic force irrespective of the nature and type of ions and the atoms or molecules involved. The magnitude of this electrostatic force is secular in that its magnitude is determined by an inverse square law – whatever be the context and location.