We gain some insight into the nature of physics by exploring the story of physics from its beginnings until now, relating our knowledge of phenomena to general principles and using these established principles to explore an ever expanding list of applications. The progress of physics depends on a continuing interaction between experiment and theory. Weighing balance is the most common example for application of simple principle of 'Lever' discovered by Aristotle. The process of arriving at general principles to describe how the nature behaves continues to find limitations in the range of validity of the theories.
The journey in Physics is all the more exciting as no theory is taken to be final. New observations or evidence inconsistent with known theory can force original theory to be revised or discarded. For example, Ptolemy believed earth to be the center of universe until Copernicus proved it otherwise. Building on the Copernican idea of earth's revolution around the sun, Johannes Kepler proceeded to formulate the laws regarding planetary motions. In addition, Kepler also stated that the planetary orbits are elliptical rather than circles – a fact still accepted.
