Physics is a branch of science. The word 'physics' has come from Greek word meaning nature. Thus, Physics is the subject of studying nature and natural phenomena.
The knowledge of science is acquired through a method consisting of the following four steps:
- observation of facts
- proposing theory or hypothesis to explain the observation
- testing the validity of the theoretical predictions based on the proposed theory
- modification of the theory, if necessary
All these steps taken together constitute the scientific method.
It may happen that a new observation or a new measurement shows a discrepancy between an existing theory and the observation. Then the theory is to be modified or even to be replaced by a new theory. Following examples may be cited for this:- The old concept of flat earth was replaced by the concept of spherical earth from the observation of distant ships in a sea. Further, to account for the small variations in the value of 'g' at various places on earth, the shape of the earth had to be considered as oblate spheroidal.
- The geocentric theory imagining earth to be at the centre of the universe was replaced by the heliocentric theory imagining sun to be stationary and all planets including earth revolving around it. This was done to account for astronomical observations of Copernicus and Galileo.
- Newton proposed corpuscular theory of light on the basis of his observations of shadow formation. Later on, to explain diffraction of light by small obstacles, Newton's theory was replaced by Huygen's wave theory of light. When photoelectric effect was discovered, an entirely new-concept theory, the quantum theory of light, was developed to explain it. Finally, de Broglie gave the concept of dual nature of light to explain all phenomena regarding light.
- Newton's equations of motion failed to explain the motion of bodies moving at very high speeds, close to the speed of light. Then, Einstein's theory of relativity using entirely new concepts regarding space and time came into existence. All predictions of this theory have been experimentally confirmed.
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