Newton's Law of Universal Gravitation power point for conceptual physics students with little math background.

1. Gravity
Newton rationalized that if the earth puts a force
on an apple, then who’s to say that it doesn’t
exert a force on the moon?
Contact vs. Non-contact Forces
↓  Newer concept: force
Must be touching acting at a distance
(gravity, magnets,
electricity…)

2. Gravity must be
proportional to both
masses because of
Newton’s 3rd
Law
(Equal and opposite
forces)
F α M m
Newton’s Math Proof
Force of gravity must
decrease by the
inverse square of the
distance.
F α 1/r2
This is known as the
inverse square law!
It is repeated in
electricity and
magnetism!
Combine
These!
2
Mm
F
r
α 2
GMm
F
r
=

3. Law of Universal Gravitation
Every particle in the universe attracts every other
particle with a force that is proportional to the
product of their masses and inversely
proportional to the square of the distances
between them. This force acts along a line
joining the 2 particles.
2
GMm
F
r
=
G = gravitational constant (small or large?)
G = 6.67 x 10-11
Nm2
/kg2
It took 100 years later for this law to be proven.
Henry Cavendish performed the experiment.

4. Sample Problem
A 50 kg girl & a 70 kg boy are 50 cm apart on a
park bench. Find the force of attraction…
Field  Area around an
object that affects
other objects.
Gravitational Field
 Area around a
mass that affects
other masses
What represents the
gravitational field around the
earth?
At Crown Point, the radius
of the Earth is 6.37101 x
106
m. If the Earth has a
mass of 5.98 x 1024
kg.
Then calculate the Earth’s
gravitational field in Crown
Point.
11 24
2 6 2
2
6.67 10 (5.98 10 )
(6.37101 10 )
9.83 /
GM x x
g
r x
g m s
−
= =
=