Transcript Slide 1

Aim: How can we explain Newton’s
Universal Law of Gravitation?
Do Now:
Why does the moon orbit the Earth?
You will know by the end of the lesson
Gravity
Gravity
is a universal law.
Should behave the same
where ever you are in the
universe.
It's a force of attraction that
exists between any two
objects that have mass.
Gravity: similar to another
force of attraction
Love… aww
The
greater the mass,
the more force of
attraction
The closer the
objects, the greater
the force of attraction
m1 & m2 = masses of 2 objects
r = distance between the centers of the 2 objects
What about G?
G is the Gravitational
Constant
What does G equal and where can we find it?
How does G compare to g?
For an object
on the Earth:
= 9.8 m/s2
Hence, Fg = mg
Problems
What is the force of attraction between two football
players (m1 = 80 kg and m2 = 100 kg) that are
standing 1 m apart?
Fg = 5.4 x 10-7 N
Not much attraction!
What is the force of attraction between the Earth
and the Moon?
Fg = 2.0 x 1020 N
Now that’s a big attraction!
So why doesn’t the Moon fall to the Earth?
It is falling!
It also has a
velocity vector
tangent to the
Earth
What is the
resultant?
An orbit!
Why Doesn’t the Moon Fall Down
How is Fg proportional to m1 and m2?
They are directly proportional
If one goes up, the other goes up
What happens to the force if:
mass
force
double m1
2F
triple m2
3F
double m1 and m2
4F
triple m1 and m2
9F
½ m1
½F
½ m1 and m2
¼F
The trick:
•Start with easy numbers
•Manipulate
•Solve
How is Fg proportional to r?
They are indirectly proportional
If one goes up, the other goes down
What happens to the force if:
distance
force
double r
¼F
triple r
1/9 F
½r
4F
1/3 r
9F
The gravitational force of attraction between two
objects is 100 N. What will be the new force if you
double m1, quadruple m2, and triple r?
The force will be 8/9 F
Fg = (8/9)(100 N)
Fg = 88.9 N