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State Kepler's laws of planetary motion....

State Kepler's laws of planetary motion.

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Johannes Kepler formulated three laws of planetary motion on the basis of observations made by astronomers.
First law (Law of orbits): The orbit of a planet is elliptical with the sun as one focus of the ellipse as shown in the figure.
Second law (Law of areas): The line joining the planet and the sun sweeps equal intervals of time. If the time of travel from A to B is the same as that from C to D, then the areas OAB and OCD are equal.
Third law (Law of periods): The cube of the mean distance r of a planet from the sun is proportional to the square of its orbital period T.
`r^(3) alpha T^2`
`r^3/T^2"= constant"`
Kepler could not give a theory to explain the motion of planets. It was Newton who showed that the cause of the planetary motion is the gravitational force that the sum exerts on them.
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