# Kepler’s laws of Planetary Motion for CBSE Class 11th

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Kepler's law of planetary motion
CBSE Class 11th
By iProf

Johannes Kepler
Johannes Kepler was a German mathematician, astronomer, and
astrologer. A key figure in the 17th century scientific revolution, he is best
known for his laws of planetary motion, based on his works Astronomia
nova, Harmonices Mundi, and Epitome of Copernican Astronomy. These
works also provided one of the foundations for Isaac Newton's theory of
universal gravitation.

Keplers's law of planetary motion
In astronomy, Kepler's laws of planetary motion are three scientific laws
describing the motion of planets around the Sun. Kepler's laws are now

Three laws of Kepler
1
Kepler's first law- Law of orbit
Kepler's second law- Law of equal areas
2
Kepler's third law- Law of periods
3

Kepler's first law- Law of orbit
Every planet revolves in an elliptical orbit around the sun. The orbit of every
planet is an ellipse with the Sun at one of the two foci.

Kepler's second law- Law of equal area
A line joining a planet and the Sun sweeps out equal areas during equal
intervals of time.This law is known as Kepler's second law.

Kepler's third law- Law of periods
The square of the orbital period of a planet is directly proportional to the cube
of the semi-major axis of its orbit.
According to Kepler's third law :P2/a3

Mathematical representation of Kepler's third law
P2/a3
`P' is the time taken for a planet to complete an orbit around the
sun
`a' is the mean value between the maximum and minimum
distances between the planet and sun

Contribution of Kepler's law
With the help of Kepler's second law, Newton introduced the Law of
universal gravitation (Newton's law of gravitation).
Kepler's laws are very useful in the study of planet orbit systems.
These laws are also very important for satellite motion.

Newton's law of universal gravitation
Newton's law of universal gravitation states that any two bodies in the universe attract
each other with a force that is directly proportional to the product of their masses and
inversely proportional to the square of the distance between them.
m
M
r
Mass of body 1
Universal gravitational
F= GmM
constant
r2
Distance between
Mass of body 2
two matter