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Physical World | Hemanth G Nag

•  Science means organized knowledge.

It is human nature to observe things and happenings
Example: Phenomena of apple falling to ground,

moon revolving around earth and weightlessness in

around in the nature and then to relate them. This

the rocket, all these phenomena are explained with

knowledge is organized so that it become well

help of one Law that is, Newtons Law of Gravitation.

connected and logical. Then it is known as Science. It

is a systematic attempt to understand natural

phenomenon and use this knowledge to predict,

•  To understand or to derive the properties of a

modify and control phenomena.

bigger or more complex system the properties

Scientific Method
of its simpler constituents are taken into

Scientific methods are used to observe things and
account. This approach is called reductionism.

It is supposed to be the heart of Physics.

natural phenomena. It includes several steps :

For example a complex thermo dynamical system can


be understood by the properties of its constituent like

Controlled experiments,

kinetic energy of molecules and atoms.

Qualitative and quantitative reasoning,

•  Mathematical modeling,

•  Prediction and
•  The scope of Physics can be divided in to two

Verification or falsification of theories.

domains; Macroscopic and Microscopic.

There  is  no  ‘final’  theory  in  science  and  no

unquestioned authority in science.
•  Macroscopic domain includes phenomena at the

level of Laboratory, terrestrial and astronomical

Observations and experiments need theories


to support them. Sometimes the existing

•  Microscopic domain I ncludes atomic, molecular

theory is unable to explain the new

and nuclear phenomena.

observations, hence either new theories are

•  Recently third domain in between is also thought

formed or modification is done in the existing

of with name Mesoscopic Physics. This deals with


group of Hundreds of atoms

For example to explain different phenomena

•  Scope of physics is very wide and exciting

in light, theories are changed. To explain

because it deals with objects of size as large

bending of light a new Wave-theory was

as Universe (1025m) and as small as 10-14 m,

formed, and then to explain photoelectric
the size of a nucleus.

effect help of quantum mechanics was taken.

The excitement of Physics is experienced in many

Natural Sciences can be broadly divided in three

fields Like:

branches namely Physics, Chemistry and biology

•  Live transmissions through television.

Physics is a study of basic laws of nature and

•  Computers with high speed and memory,

their manifestation in different phenomenas.

•  Use of Robots,

Principal thrusts in Physics

•  Lasers and their applications

There are two principal thrusts in Physics;

•   1.Unification  2. reduction
Physics in relation to other branches of Science


          Efforts are made to explain different phenomena in nature on the basis of one or minimum laws. This is principle of Unification.

Physics in relation to Chemistry.

          Chemical bonding, atomic number and complex structure can be explained by physics phenomena of Electrostatic forces,

                taking help of X-ray diffraction.

Physics in relation to other Science

          Physics in relation to Biological Sciences: Physics helps in study of Biology through its inventions. Optical microscope helps to study bio-samples, electron microscope helps to

study biological cells. X-rays have many applications in biological sciences. Radio isotopes are used in cancer.

Physics in relation with Astronomy:

          Giant astronomical telescope developed in physics are used for observing planets. Radio telescopes have enabled astronomers to observe distant limits of universe.

          Physics related to other sciences: Laws of Physics are used to study different phenomenas in other sciences like Biophysics, oceanography, seismology etc.

Fundamental Forces in Nature

There is a large number of forces experienced or applied. These may be macroscopic forces like gravitation, friction, contact forces and microscopic forces like electromagnetic and inter-atomic forces. But all these forces arise from some basic forces called Fundamental Forces.

Fundamental Forces in Nature..

1.  Gravitational force.

          It is due to Mass of the two bodies.

          It is always attractive.

          It operates in all objects of universe.

          Its range is infinite
It’s a weaktimes comparedforcetostrong.10 Nuclear force

2.Electromagnetic Forces:

          It’s due to stationery charge

          It may be attractive or repulsive.

          It operates on charged particles

          Its range is infinite

          Its stronger 1036 times than gravitational force but 10-2 times of strong Nuclear force.

3.  Strong nuclear force:

          Its range is very short, within nuclear size (10-15 m).

          Its strongest force in nature

4.Weak Nuclear force:

          Operate within nucleons I.e. elementary particles like electron and neutrino.

          It appears during radioactive b decay.

          Has very short range 10-15m.
          10-13 times than Strong nuclear force.

Conservation Laws

          In any physical phenomenon governed by different forces, several quantities do not change with time. These special quantities are

conserved quantities of nature.

1.For motion under conservative force, the total mechanical Energy of a body is constant.

2.Total energy of a system is conserved, and it is valid across all domains of nature from microscopic to macroscopic. Total energy of the universe is believed to be constant.

3.Conservation of Mass was considered another conservation law, till advent of Einstein. Then it was converted to law of conservation of mass plus energy. Because mass is converted into energy and vice-versa according to equation E = mc2 The examples are annihilation and pair production.

4.Momentum is another quantity which is preserved. Similar is angular momentum of an isolated system. 5.Conservation of Electric charge is a fundamental law of nature.

6. Later there was development of law of conservation of attributes called baryon number, lepton number and so on.

or  moving  Electrical

The laws of nature do not change with change of space and time. This is known as symmetry of space and time. This and some other symmetries play a central role in modern physics. Conservation laws are connected to this.

          Operate between Nucleons

          It may be attractive or repulsive