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1
Spring 2004
PHY 2053C: College Physics A
Today:
finish:
Dynamics:
of
Circular
Motion, Gravity
Circular Motion
Newton: Gravity
Satellites &
“Weightlessness”
start:
Work and Energy
Conserved quantities
Work
Kinetic and Potential
Energy
L8—Ch5,Ch6
NOTE:
I wont be giving
back the tests today.
They weren’t sorted
alphabetically before I
got them this morning.
We’ll go over it on Wed.
(Reminder)
Important Points from last Lecture
Uniform circular motion implies presence of a
“
Centripetal Force
”
This force can be delivered by
friction
,
norma
l,
gravity
or any other
force
you can think of.
Gravity
is a general force between any objects
with
mass
For
orbital motion
(planets, moon, satellites),
gravity provides the centripetal force:
F
G
G
m
1
m
2
r
2
G
m
1
m
2
r
2
m
1
v
2
r
<=>
G
m
2
2
2
r
3
T
2

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(reminder)
Gravity
r
m
m
G
F
=
2
More
mass
, either one,
means more
force
Greater
separation
means less
force
Gravity
is an attractive
force
acts
along the line between two objects.
The
force
is proportional to the
product of the two
masses
.
1
m
Newton’s Law of Universal Gravitation:
2
m
F
F
r
The
force
is inversely proportional
to the square of the
distance
between the masses.
Important –
BOTH
objects feel this
force, and are attracted to each other.
Satellite Orbits
“Newton’s Cannon”
Newton devised a
“thought experiment”
to explain how satellites stay in orbit.
A cannonball travels over the ground as it
falls
toward Earth.

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