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ോ, , ോ, , ോ, , 1. PHYSICAL WORLD, , ോ, , ോ, , • Science means organized knowledge., It is a systematic attempt to understand natural, phenomenon and use this knowledge to predict,, modify and control phenomena., Scientific Method, Scientific methods are used to observe things and, natural phenomena. It includes several steps :, • Observations, • Controlled experiments,, • Qualitative and quantitative reasoning,, • Mathematical modelling,, • Prediction and, • Verification or falsification of theories., Science can be broadly divided into physical, science and biological science. The main branches, of Physical science are physics and chemistry., • Physics is a study of basic laws of nature and, their manifestation in matter and energy., Principal thrusts in Physics, • There are two principal thrusts in Physics;, • 1.Unification 2. reduction, Unification, • Efforts are made to explain different, phenomena in nature on the basis of one or, minimum laws. This is principle of Unification., Reductionism, • To understand or to derive the properties of a, bigger or more complex system the properties, of its simpler constituents are taken into, account. This approach is called reductionism., • The scope of Physics can be divided in to two, domains; Macroscopic and Microscopic., • Macroscopic domain includes phenomena at the, level of Laboratory, terrestrial and astronomical, scales., • Microscopic domain I includes atomic, molecular, and nuclear phenomena., Physics in relation to other branches of Science, 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 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., , seismology etc., , 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, phenomena in other sciences like Biophysics,, oceanography, 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 weak force. 10-38 times compared to strong, Nuclear force, 2.Electromagnetic Forces:, • It’s due to stationery or moving Electrical, 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:, • Operate between Nucleons, • It may be attractive or repulsive, • 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.

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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, ., 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.