PHYSICAL WORLD

                      1. Introduction

In this we will learn the full topic about physical world. To know about "What is physics" And about "Scopes of physics" Click on the above link. The word Science originates from the Latin word S c i e n t i a meaning ‘to know’ , ‘knowledge’. Science, in a broad sense, is as old as human species. The early civilisations of Egypt, India, China, Greece, Mesopotamia and many others made vital contributions to its progress. From the sixteenth century onwards, great strides were made in science in Europe. The interplay of theory and observation (or experiment) is basic to the progress of science. Science is ever dynamic. There is no ‘final’ theory in science and no unquestioned authority among scientists. As observations improve in detail and precision or experiments yield new results, theories must account for them, by introducing modifications. 

The modifications may not be drastic and may lie within the framework of existing theory. For example, when Johannes Kepler (1571-1630) examined the extensive data on planetary motion collected by Tycho Brahe (1546-1601), the planetary circular orbits in heliocentric theory (sun at the centre of the solar system) imagined by Nicolas Copernicus (1473–1543) had to be replaced by elliptical orbits to fit the data better. Occasionally, however, the existing theory is simply unable to explain new observations. This causes a major upheaval in science. In the beginning of the twentieth century, it was realised that Newtonian mechanics, till then a very successful theory, could not explain some of the most basic features of atomic phenomena. 

Similarly, the then accepted wave picture of light

failed to explain the photoelectric effect properly.

This led to the development of a radically new

theory (Quantum Mechanics) to deal with atomic

and molecular phenomena.  

2. PHYSICS, TECHNOLOGY AND SOCIETY

Physics, technology and the society is inter connected to each other. Physics deals with the research of our surrounding, space, planets. And this is possible with advanced new technologies. And those people who develops new technology belongs to the society. So, we can simply say that PHYSICS, TECHNOLOGY AND SOCIETY are interconnected to each other. The connection between physics, technology and society can be seen in many examples. The discipline of thermodynamics arose from the need to understand and improve the working of heat engines. The steam engine, as we know, is inseparable from the Industrial Revolution in 

England in the eighteenth century, which had

great impact on the course of human civilisation. Sometimes technology gives rise to new physics; at other times physics generates new technology. An example of the latter is the wireless communication technology that followed 

the discovery of the basic laws of electricity and

magnetism in the nineteenth century. The

applications of physics are not always easy to

foresee. As late as 1933, the great physicist

Ernest Rutherford had dismissed the possibility

of tapping energy from atoms. But only a few

years later, in 1938, Hahn and M e i t n e r

discovered the phenomenon of neutron-induced

fission of uranium, which would serve as the

basis of nuclear power reactors and nuclear

weapons. Yet another important example of

physics giving rise to technology is the silicon

‘chip’ that triggered the computer revolution in

the last three decades of the twentieth century.

A most significant area to which physics has

and will contribute is the development of

alternative energy resources. The fossil fuels of

the planet are dwindling fast and there is an

urgent need to discover new and affordable

sources of energy. Considerable progress has

already been made in this direction (for

example, in conversion of solar energy,

geothermal energy, etc., into electricity), but

much more is still to be accomplished.

Table1.1 lists some of the great physicists,

their major contribution and the country of

origin. You will appreciate from this table the

multi-cultural, international character of the

scientific endeavour. Table 1.2 lists some

important technologies and the principles of

physics they are based on. Obviously, these

tables are not exhaustive. We urge you to try to

add many names and items to these tables with

the help of your teachers, good books and

websites on science. You will find that this

exercise is very educative and also great fun.

And, assuredly, it will never end. The progress

of science is unstoppable! Physics is the study of nature and natural phenomena. Physicists try to discover the rule that are operating in nature, on the basis of observations, experimentation and analysis. Physics deals with certain basic rules / laws governing the natural world.  

  3. FUNDAMENTAL FORCES IN NATURE

As we know force is needed to push, carry or 

throw objects, deform or break them. We also

experience the impact of forces on us, like when

a moving object hits us or we are in a merry-go-

round. Going from this intuitive notion to the

proper scientific concept of force is not a trivial

matter. Early thinkers like Aristotle had wrong

ideas about it. The correct notion of force was

arrived at by Isaac Newton in his famous laws of

motion. He also gave an explicit form for the force for gravitational attraction between two bodies. In the macroscopic world, besides the 

gravitational force (the force with which earth attracts an body), we encounter several kinds

of forces: muscular force(the amount of force applied by the muscles , contact forces between

bodies, friction (which is also a contact force

parallel to the surfaces in contact), the forces

exerted by compressed or elongated springs and

taut strings and ropes (tension), the force of

buoyancy and viscous force when solids are in

contact with fluids (between fluids and the container in which it kept), the force due to pressure of a fluid, the force due to surface tension of a liquid, and so on. There are also forces involving charged and magnetic bodies. In the microscopic domain again, we have electric and magnetic forces, nuclear forces involving protons and neutrons, interatomic and intermolecular forces, etc. We shall get familiar with some of these forces in later parts of this course. A great insight of the twentieth century physics is that these different forces occurring in different contexts actually arise from only a small number of fundamental forces in nature. For example, the elastic spring force arises due to the net attraction / repulsion between the neighbouring atoms of the spring when the spring is elongated/compressed. This net attraction / repulsion can be traced to the (unbalanced) sum of electric forces between the charged constituents of the atoms. In principle, this means that the laws for 'derived’ forces (such as spring force, friction) are not independent of the laws of fundamental forces in nature. The origin of these derived forces is, however, very complex. At the present stage of our understanding, we know of four fundamental forces in nature. 

» Gravitational Force

» Electromagnetic Force

» Strong Nuclear Force

» Weak Nuclear Force

   
  4. NATURE OF PHYSICAL LAWS

Physicists explore the whole universe. Their investigations are mainly based on scientific processes, proves range from particles that are smaller than atoms in size to stars that are very far away. In addition to finding the facts by observation and experimentation, physicists attempt to discover the laws that summarise (often as mathematical equations) these facts. In any physical phenomenon governed by different forces, several quantities may change with time. A remarkable fact is that some special physical quantities, however, remain constant in time. They are the conserved quantities of nature. Understanding these conservation principles is very important to describe the observed phenomena quantitatively. For motion under an external conservative force, the total mechanical energy i.e. the sum of kinetic and potential energy of a body is a constant. The familiar example is the free fall of an object under gravity. Both the kinetic energy of the object and its potential energy change continuously with time, but the sum remains fixed. If the object is released from rest, the initial potential energy is completely converted into the kinetic energy of the object just before it hits the ground. This law restricted for a conservative force should not be confused with the general law of conservation of energy of an isolated system (which is the basis of the First Law of Thermodynamics). The law of conservation of energy is thought to be valid across all domains of nature, from the microscopic to the macroscopic. It is routinely applied in the analysis of atomic, nuclear and elementary particle processes. At the other end, all kinds of violent phenomena occur in the universe all the time. Yet the total energy of the universe (the most ideal isolated system possible !) is believed to remain unchanged. Until the advent of Einstein’s theory of relativity, the law of conservation of mass was regarded as another basic conservation law of nature, since matter was thought to be indestructible. It was (and still is) an important principle used, for example, in the analysis of chemical reactions. A chemical reaction is basically a rearrangement of atoms among different molecules. The concept of energy is central to physics and the expressions for energy can be written for every physical system. When all forms of energy e.g., heat, mechanical energy, electrical energy etc., are counted, it turns out that energy is conserved. The general law of conservation of energy is true for all forces and for any kind of transformation between different forms of energy. In the falling object example, if you include the effect of air resistance during the fall and see the situation after the object hits the ground and stays there, the total mechanical energy is obviously not conserved. The general law of energy conservation, however, is still applicable. The initial potential energy of the stone gets transformed into other forms of energy : heat and sound. (Ultimately, sound after it is absorbed becomes heat.) The total energy of the system (stone plus the surroundings) remains unchanged.If the total binding energy of the reacting molecules is less than the total

binding energy of the product molecules, the

difference appears as heat and the reaction is

exothermic. The opposite is true for energy

absorbing (endothermic) reactions. However,

since the atoms are merely rearranged but not

destroyed, the total mass of the reactants is the

same as the total mass of the products in a

chemical reaction. The changes in the binding

energy are too small to be measured as changes

in mass. According to Einstein’s theory, mass m is

equivalent to energy E given by the relation

E = m c², where c is speed of light in vacuum.

In a nuclear process mass gets converted to

energy (or vice-versa). This is the energy which

is released in a nuclear power generation and

nuclear explosions.