Download Day 11

Announcements
•Next observing Night is a Dark Sky Night
one week from Wednesday on February 22
and then again on Monday February 27
•Be thinking about your project topic. I need
to approve your topic before spring break.
•Exam 1 will be returned next time. Still
grading the essays.
Kepler developed three laws of
planetary motion based on
Tycho’s data on Mars
Kepler’s
st
1
Law
The Law of Ellipses
The planets
move in
elliptical
orbits with
the Sun
located at
one focus
Major change since everyone that came before
had used circles, including Copernicus
Kepler’s
nd
2
Law
The Law of Areas
A line drawn
from a planet
to the Sun will
sweep out
equal areas in
equal time
periods
Kepler’s
Law
rd
3
The Law of
Harmonies
The ratio of the
square of the orbital
period to the cube of
the orbital semimajor
axis (the radius) is
the same for all the
planets
Galileo Galilei
•1564 – 1642
•First to turn the telescope
skyward
•Developed new physics to
replace the physics of
Aristotle
•Got into deep trouble with
the Catholic Church
Galileo’s first
major
discovery
concerned the
planet Jupiter
Over a week long period
in January 1610 he makes
observations that prove
the existence of four
moons orbiting Jupiter.
Another of his observations that
support the Copernican views is
the phases of Venus
In late 1632, Galileo’s book
Dialogues is banned and he is put
on trial by the Inquisition
In June 1633 he is found guilty and
sentenced to prison. After recanting
his views, his sentence is
commuted to house arrest
If you ask a physicist, Galileo’s
most important contributions were
in mechanics
Newton’s Mechanical Universe
Isaac Newton
(1643 – 1727)
Newton’s home: Woolsthorpe in
Lincolnshire
Newton’s
most
important
work
Newton was 43 years
old when the Principia
was finally published.
Most of the work for it
was done when he
was in his early 20’s
Newton’s First Law: The Law of
Inertia
An object in uniform motion (straight line at constant speed) will
maintain that motion unless acted on by some external force.
Newton’s Second Law:
The Force Law
The acceleration an object experiences is directly
proportional to the net force acting on it and inversely
proportional to the objects mass.
F = ma
Newton’s Third Law: The ActionReaction Law
For every force there is an equal and opposite reaction force.
Newton’s Law of Universal
Gravitation
Two bodies 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
their centers
Newton related the acceleration
experienced by a falling apple to
that experienced by the moon
rEarthmoon  60rEarth
1
amoon  3600
aapple
Galileo had measured the
acceleration of a falling body
near the surface of the
Earth. Newton calculated the
acceleration needed to keep
the moon in orbit (centripetal
acceleration).
A few colored card questions
ClassAction website Renaissance Astronomy
module
Gravity Fundamentals…options 1 & 3
Gravity Directions…both options
Earth Force vs. Sun Force
Forces and Motion
Discussion Questions:
Applying Newton’s Laws 2