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Question
State and explain Kepler's laws of planetary motion. Draw diagrams to illustrate these laws.
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Solution
- Kepler's first law: The planets move in elliptical orbits around the sun, with the sun at one of the two foci. of the elliptical orbit. This law means that the orbit of a planet around the sun is an ellipse and not an exact circle. An elliptical path has two foci, and the sun is at one of the two foci of the elliptical path.
- Kepler's Second law: Each planet revolves around the sun in such a way that the line joining the planet to the sun sweeps over equal areas in equal intervals of time. This means that a planet does not move with constant speed around the sun. The speed is greater when the planet is nearer the sun and less when the planet is farther away from the sun.
- Kepler's Third Law: The cube of the mean distance of a planet from the sun is directly proportional to the square of time it takes to move around the sun. r3 ∝ T2.
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