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Sir Isaac Newton and the

Unification of Physics & Astronomy

Sir Isaac Newton (1642-1727) was by many standards the most important figure in the
development of modern science. Many would credit he and Einstein with being
the most original thinkers in that development.

## The Accomplishments of Newton

Newton's accomplishments were of
astonishingly broad scope. For example, as a sidelight to his fundamental
contributions
in physics and astronomy, he (in parallel with Liebnitz) invented the
mathematical discipline of calculus, so if you have to take both physics and
calculus courses, you have Newton to blame!
No survey course such as this one
can possibly do justice to what Newton accomplished.
We shall concentrate on three developments of most direct relevance to our
discussion: (1) Newton's Three Laws of Motion,
(2) the Theory of Universal Gravitation, and (3) the demonstration that
Kepler's Laws follow from the Law of Gravitation.
## The Great Synthesis of Newton

Kepler
had proposed three Laws of Planetary motion based on the systematics that he found
in Brahe's data.
These Laws were supposed to apply only to the motions of the planets; they said
nothing about any other motion in the Universe. Further, they were purely
empirical: they worked, but no one knew a fundamental reason WHY they
should work.
Newton changed all of that. First, he demonstrated that
the motion of objects on the Earth could be described by three new Laws of
motion, and then he went on to show that Kepler's three Laws of Planetary Motion
were but special cases of Newton's three
Laws if a force of a particular kind (what
we now know to be the gravitational force) were postulated to exist between
all objects in the Universe having mass. In fact, Newton went even further:
he showed that Kepler's Laws of planetary motion were only approximately
correct, and supplied the quantitative corrections that with careful
observations proved to be valid.

## References

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