1. Gravity and Motion Chapter 19 section 2

2. Isaac Newton realized that there must be a force acting between Earth and the moon that kept the moon in orbit Force- a push or pull ◦ Most everyday forces require objects to be in contact, but the moon in orbit is a force that acts over long distances that are not in orbit

3. Gravity- a force that attracts all objects toward each other ◦ While Newton did not discover gravity, he was the first person to realize that gravity occurs everywhere ◦ Force of gravity is measured in a unit called newtons Law of Universal Gravitation- every object in the universe attracts every other object

5. Mass and Weight The strength of the force of gravity between two objects depends on two factors: the masses of the objects and the distance between them Mass- the amount of matter in an object ◦ The strength of gravity depends in part on the masses of each of the objects Weight- the force of gravity on an object ◦ Can change depending on location The force of gravity decreases rapidly as distance increases

6. Motion Inertia- the tendency of an object to resist a change in motion ◦ The more mass an object has, the greater its inertia Newton’s first law of motion- an object at rest will stay at rest and an object in motion will stay in motion with a constant speed and direction unless acted on by a force

7. Newton concluded that two factors- inertia and gravity- combine to keep Earth in orbit around the sun and the moon in orbit around Earth