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CBSE - IX
Kepler's Law of Gravitation
KEPLER'S LAW OF GRAVITATION
The universe is one of the most fascinating subjects that were explored by many people around the world. Johannes Kepler, a student of Tyco Brahe, suggested three laws about the motion of the planets in the solar system, which revolutionised the comprehension about our solar system. These laws are named after him as Kepler’s laws of planetary motion. The first law of Kepler enunciates that the shape of the orbits of the planets revolve around the Sun in an ellipse and not a circle as thought till then. This first law is referred to as the law of orbits. The second law tells us about the area swept by the line joining a planet and the sun. According to Kepler’s second law, the line joining the Sun and a planet covers equal areas in equal
intervals of time. This law is referred to as the law of equal areas.The speed of a planet in its orbit varies with its distance from the Sun. At perihelion, the position where the planet is closest to the Sun, the speed of the planet in its orbit is the maximum. On the other hand, at aphelion, the position where the planet is farthest from the Sun, the speed of the planet is the slowest. Kepler’s third law tells us about the average radius of the orbit of a planet and its period of revolution. According to the third law, which is referred to as the law of periods, the square of the period of revolution of the planet is proportional to the cube of the average radius of the planet’s orbit.
