Announcements
•Next exam is scheduled for Thursday March
24. Will cover Chapters 6 & 7 and possibly
some of Chapter 8. Sample questions will be
posted this week.
•Dark Sky Observing Nights next week on
Monday and Wednesday. Forecast doesn’t
look good for either or the alternate day on
Thursday. If we go, set-up starts at 6:30pm. If
needed, I’ll post a cancellation notice on
APSU Astronomy by 5:00pm on the day of
the observing.
In 1660 the
Greshamites
form the
Royal
Society
The Philosophical
Transactions of the Royal
Society have been
published since 1665 and
are available online
Robert Hooke is the Curator of
Experiments for the Royal Society
Known as London’s
Leonardo because of
his involvement in the
rebuilding of London
after the great fire of
1666. His experiments
on the pendulum gave
rise to Hooke’s Law.
Check out the official
Robert Hooke website
Hooke postulates an attractive
force between the Sun and planets
that diminishes with distance
He never showed
it was an inverse
square law, just
an inverse law of
some sort.
In a series of letters, Hooke spurred
Newton into thinking about Gravity
Hooke’s “discussions” with Newton became somewhat
critical of Newton’s ideas. As a result, Newton despised
Hooke and eventually tries to erase all traces of him
from the Royal Society records
Isaac Newton
1642 – 1727
Born at Woolsthorpe
Manor in Lincolnshire
three months after his
father dies. He is
raised by his maternal
grandmother after his
mother remarries. He
isn’t nobility but he
does have status
above the peasantry
Early on, his mother wants him
to run the farm
Isaac absolutely hates
farming and openly
shows his dislike of it
Fortunately, the local school master convinces Isaac’s
mother to send him back to school. Eventually, he enters
Trinity College at Cambridge in 1661.
In 1665 Plague hits London and
Newton goes home to
Woolsthorpe
While at home he continues
his studies on his own. It is
during these two year that he
forms his early ideas about
light, motion, gravity and the
foundations of calculus. He is
still very much a Cartesian at
this time but he is beginning
to question it.
In 1669 Newton is appointed the
Lucasian Chair of Mathematics at
Trinity College in Cambridge
The chair is currently held by Steven Hawking
Due to an early “run-in” with
Hooke over the behavior of
light, Newton becomes a
recluse at Cambridge
By 1684 Hooke, Wren and
Halley are in discussions on the
nature of the force binding the
solar system
Edmund Halley decides to visit
Newton and asks about orbits
After Newton sends Halley a 9
page proof that the orbits are
ellipses, Halley starts pushing
Newton to publish his work
Newton’s first draft contained his 1st
Law of motion and an inverse
square law of gravity
He still had not figured out his 3rd Law and his law of
gravity was a little fuzzy with only an inverse square
distance relationship
His second draft brought him to his
3rd Law and the mutual nature of
the force of gravity
He immediately saw the
problem that it would be
impossible to calculate
precisely the orbit of any
planet with all the other
planets and the Sun pulling
on every other object
His biggest hurtle was
determining the force of gravity
of an extended object
It is this problem that leads him to the invention of calculus
He proved the universality of his
law of gravity by comparing the fall
of an apple to the “fall” of the moon
His next proof was to explain the
complicated lunar orbit
Newton is also able to derive all
three of Kepler’s Laws
Just before he was ready to publish,
Hooke tried to interject himself
As a result, Newton makes
much of his work overly
mathematically complicated,
beyond anything Hooke
could understand
Halley must do a great deal
of soothing to calm Newton
down and convince him to
complete the work
Finally, Principia is published in
July 1687
It is an exceedingly difficult
book to read with lots of
overly complicated math. It is
not a book that could be used
to teach others physics.
A 2nd Edition is published
in 1713 and a 3rd Edition is
published in 1726
Thanks to Samuel Clarke’s edition
of Jacques Rohault’s Treatise of
Physics an understandable bit of
Newtonianism came out
Once others got into the act, more
proofs of universal gravity and
Newton’s laws came about
The Paris Academy of Science attempted to decide
between the shape of the Earth as predicted by
Descartes and that predicted by Newton using the
lengths of pendulums. Their results were inconclusive
The most triumphant proof was by
Edmund Halley and his prediction
of the return of his comet
Halley noted the orbits of the comets of 1682, 1607 and 1531
were all very similar. His calculations show they are all one
object and he predicts it will return in 1758
Halley’s prediction was improved
by Alexis-Claude Clairaut
The problem was the
perturbing influence of
Jupiter. Clairaut’s
prediction was only a
month off in perihelion
The biggest problem with universal
gravitation was the 3-body problem
Many of the most famous
mathematicians of the 18th and 19th
Centuries worked on the problem
Jean D’Alembert
Joseph
Lagrange
Leonhard
Euler
Simon de
Laplace
After the publication of Principia,
Newton moves on
He serves as Master of the Mint from 1699 for almost
30 years until his death in 1727
He is knighted by Queen Anne
in 1705
He also serves two
unremarkable term in
Parliament as the member
from Cambridge 1689 –
1690 and 1701 - 1702
Newton dies on March 20, 1727
He is buried in Westminster Abby