Physical World Units and measurements

 PHYSICAL WORLD

• SCIENCE:

The word science has been derived from a Latin word ‘scientia’ which means ‘to know’. Hence, science may be defined as the systematic study of facts, events and happenings around us is called science.

• PHYSICS:

The word physics has been derived from a Greek word ’fusis’ which means ‘nature’. Hence, physics may be defined as the branch of science which deals with the study of nature and natural phenomena.

• SCIENTIFIC METHOD:

To know fully about anything we have to use the following steps:
1. Systematic observations
2. Controlled experiments
3. Qualitative and quantitative reasoning
4. Mathematical modeling
5. Prediction and verification of theories
These steps taken together are known as scientific method.

• UNIFICATION

Effort to explain different physical phenomena in terms of a few concepts and laws in physics is known as
unification. For example, the same law of gravitation  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.

• REDUCTION

Effort is to derive the properties of a bigger, more complex, system from the properties and interactions of its
basic simpler parts is called reduction or reductionism. For example, the subject of thermodynamics, developed in the nineteenth century, deals with bulk systems in terms of macroscopic quantities such as temperature, internal energy, entropy, etc.

• SCOPE OF PHYSICS

The idea of scope of physics can be obtained by study of following three domains  in physics:
1. Macroscopic domain: It deals with the study of large bodies and their phenomena. E.g. astronomical
phenomena and terrestrial phenomena.
2. Microscopic domain: it deals with the study of very small particles like electron, protons, neutrons, α-
particles and structure of atom.
3. Mesoscopic domain: It deals with the study of a few tens or hundreds of atoms.
It covers a very large range of magnitude of physical quantities like length, mass, time, energy, etc.
e.g. range of length is from 10 race to power-14m (study of electrons etc.) to 1026m (size of universe).Range of time is from 10 race to power -22s (time taken by light to cross nuclear diameter) to 10 race to power18s ( age of sun).The range of masses goes from, 10 race to power-30 kg (mass of an electron) to 10 race to power 55 kg (mass of known  observable universe)

• EXCITEMENT OF PHYSICS

Physics is exciting in many ways as-
1. A large number of complex phenomena of nature can be explained on the basis of some fundamental
laws of physics.
2. Physics has opened and detected many secrets of nature.
Except these reason for excitement of physics can vary from person to person.

• HYPOTHESIS, AXIOMS AND MODELS

A hypothesis is a supposition without assuming that it is true. It cannot be proved but it can be verified. e.g. The universal law of gravitation, because it cannot be proved. It can be verified and substantiated by experiments and observations. An axiom is a self-evident truth Model is a theory proposed to explain observed phenomena. For example Bohr’s model of hydrogen atom, in which Bohr assumed that an electron in the hydrogen atom follows certain rules

• PHYSICS, TECHNOLOGY AND SOCIETY

Technology is the application of the laws in physics for practical purposes.
The invention of steam engine, nuclear reactors, Production of electricity from solar energy and geothermal
energy had a great impact on human civilization. Also, physics giving rise to technology is the integrated chip( IC) and processors which grew the computer industry greatly in the last two decades. Computers have improved production techniques and lower production costs. The lawful purpose of technology is to serve people. Our society is becoming more and more science-oriented. We can become better members of society by understanding of the basic laws of physics.

• LINK BETWEEN TECHNOLOGY AND PHYSICS

Technology Scientific principle(s)
Aeroplane Bernoulli.s principle in fluid dynamics
Computers Digital logic
Electric generator Faraday.s laws of electromagnetic induction
Electron microscope Wave nature of electrons
Hydroelectric power Conversion of gravitational pot. energy into electrical energy
Lasers Light amplification by stimulated emission of radiation
Non-reflecting coatings Thin film optical interference
Nuclear reactor Controlled nuclear fission
Optical fibers Total internal reflection of light
Particle accelerators Motion of charged particles in electromagnetic fields
Photocell Photoelectric effect
Production of ultra high magnetic fields Superconductivity
Radio and Television Generation, propagation and detection of e.m. waves

• FUNDAMENTAL FORCES IN NATURE

Sir Issac Newton was the first who give an exact definition for force.“Force is the external agency applied on a body
to change its state of rest and motion”.
There are four basic forces in nature.
1. Gravitational force
2. Electromagnetic force
3. Strong nuclear force and
4. Weak nuclear force.

• 1. Gravitational force

Newton’s law of gravitation, the gravitational force of attraction between any two bodies in universe is directly
proportional to the product of the masses and inversely proportional to the square of the distance between them.
Properties:
1. It is the force between any two objects in the universe.
2. It is an attractive force by virtue of their masses.
3. By Gravitational force is the weakest force among the fundamental forces of nature but control the
structure of universe
4.  Unlike the other forces, gravity works universally on all matter and energy, and is universally attractive.
5. Carrier of these forces is Graviton.

• 2. Electromagnetic force

It is the force between charged particles such as the force between two electrons, or the force between two
current carrying wires.
Properties:
1. It is attractive for unlike charges and repulsive for like charges.
2. The electromagnetic force obeys inverse square law.
3. It is very strong compared to the gravitational force.
4. It is the combination of electrostatic and magnetic forces.
5.Carrier of these forces is Photon.

• 3. Strong nuclear force

This force holds the protons and neutrons together in the nucleus of an atom. It is the strongest of all the basic forces of nature. It, however, has the shortest range, of the order of 10−15 m. Carrier of these forces are mesons and pions.

• 4. Weak nuclear force

Weak nuclear force is important in certain types of nuclear process such as β-decay. This force is stronger than the gravitational force but much weaker than strong nuclear force.