He carried mathematization of data from
experiments as far as possible. His universal theory of
gravitation is based on the idea of forces between objects rather
than from one object to another; e.g. the apple exerts a force
toward the earth as well as receiving a force from the earth. His
law of gravitation explains how the whole universe is held
together. This law holds that every object in the universe
attracts every other object with a single gravitational force that
is directly proportional to the product of their masses and
inversely proportional to the square of the distance between their
centers. Newton had first believed in the Cartesian system of
celestial vortices of aether than swirled the planets and comets
around their orbits. The gross features of the universe led to his
recognition that the attraction between two bodies decreased
inversely to the square of the distance between them. Then he came
to accept Hooke's hypothesis that planets are kept in their orbits
by the combination of an attractive power of the sun and of motion
in a straight line that was tangential to their orbits. From
astronomical data, he calculated this centrifugal acceleration of
each planet to be the inverse square of its distance from the sun.
He also calculated the "centripetal" accelerations necessary to
bring the planets into their orbits. His experiments had shown
that he centripetal force in a circular orbit was equal to the
mass of the body times the square of its velocity, all divided by
the radius of the circular path.
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