1. Newton’s Law of Gravity
The man who answered the why to Kepler’s Laws

2. SPI’s
GLE Identify factors that influence the amount of gravitational force between objects.
GLE Recognize that gravity is the force that controls the motion of objects in the solar system.

3. Review of Gravity Gravity is a force that holds everything in place
Everything has gravity
Gravity pulls us to the center of whatever object we are standing on
For example we are being “pulled” towards the center of the Earth
The Earth is being “pulled” towards the center of the sun

4. Law of Universal Gravitation
States that the force of gravity depends on the product of the masses of the objects divided by the square of the distance between the objects
This means that mass of an object and distance from an object all have an impact on how strong gravity is

6. Law of Universal Gravitation cont.
In Simpler terms, Newton simply means:
The more massive an object the stronger its pull of gravity
The closer an object is the stronger the gravity

9. The force against Gravity
So if everything is being pulled by gravity, why do we not fall toward the sun?
Very simple we have something working against gravity
Inertia
An object’s resistance in speed or direction
An object in motion tends to stay in motion

11. So what does all this mean?
At one time Earth was moving through space
Since there is no friction in space, the Earth was content to move forever in a straight line
Then one day it moved into the gravity of the sun
The sun tries to pull the Earth towards itself and the Earth tried to pull away
The result is an orbit

13. Why does all this work?
Newton found that inertia and gravity, when working equally would cause an orbit
If one of these variables increased (or decreased) then this delicate balance would change
If Inertia of the Earth increased what do you think would happen?
We would go flying off into space
If the sun’s gravity increased what do you think would happen?
We would gradually be sucked into the sun