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

SPI’s GLE 0807.12.4 Identify factors that influence the amount of gravitational force between objects. GLE 0807.12.5 Recognize that gravity is the force that controls the motion of objects in the solar system.

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

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

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

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

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

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