Lesson 1: Gravitation ( गुरुत्वाकर्षण) English Notes: • Discovery of Gravitational Force: Sir Isaac Newton discovered the gravitational force by observing an apple fall vertically downwards. He concluded that the Earth must be attracting the apple towards its center. This force is universal, acting between any two objects in the universe. • Force and Motion: A force is necessary to change an object's speed or direction of motion. • Circular Motion and Centripetal Force: An object moving in a circular path requires a force directed towards the center, called centripetal force (F = mv²/r). This force is exerted by the Earth on the Moon, causing its orbit, and similarly by the Sun on planets. • Kepler's Laws of Planetary Motion: Based on observational data, Johannes Kepler formulated three laws describing planetary motion. 1. First Law: The orbit of a planet is an ellipse with the Sun at one of the foci. 2. Second ...