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Mechanics:

Gravity and Gravitation

Many scientist studied the planetary motion.
Ptolemy – Greek astronomer.

He advanced the theory called the Geocentric theory.

Which considered Earth as the centre of universe around which all the planet, the moon and
stars revolved in the various orbit and the theory was universally accepted for more than

fourteen centuries.

The Ptolemaic theory first challenged in 1543 by the famous Polish astronomer Nicolaus
Copernicus.

He kept the name of his theory as Heliocentric.

According to this sun was supposed to be at the centre of the universe about which other

celestial bodies revolved in various orbits. Copernicus also believed that the earth rotated on its
axis once each day.

Indian astronomer and mathematician Aryabhata said that the Earth is round and days-nights

are caused by the daily rotation of Earth upon its axis.

{ Galileo + Kepler}