1. Chapter Seven Section Two
Gravity and Motion
Chapter Seven
Section Two

2. Gravity
Definition: The attractive force between objects (Force: A push or pull)
The Law of Gravity (Newton’s Law of Universal Gravitation): Every object in the universe attracts every other object

3. The force of gravity is measured in newtons (N)
The strength of the force between two objects depends on two factors:
The masses of the objects
The distance between them

4. Gravity, Mass, and Weight
Mass: The amount of matter in an object
The greater the mass, the stronger the force of gravity
The sun>Earth>moon
Earth revolves around the sun
The moon revolves around earth

5. Gravity, Mass, and Weight
Weight: The force of gravity on an object
Weight can change depending on location
Since the moon is smaller than Earth, an object there is 1/6 its weight on Earth.
How much would you weigh on the moon?

6. Gravity, Mass, and Weight
The strength of gravity is affected by the distance between the two objects as well as their masses
Gravity increases the closer the objects are to each other
The farther away the objects are, the weaker the pull becomes

7. Inertia and Orbital Motion
Inertia keeps the Earth from crashing into the sun, and the moon from crashing into Earth
Inertia: The tendency of an object to resist motion
Newton’s First Law of Motion: An object at rest will stay at rest and an object in motion will stay in motion with constant speed and direction unless acted on by a force.
Inertia and gravity combine to keep the Earth in orbit around the sun and the moon in orbit around the earth.

8. Inertia and Orbital Motion
Think of Earth as the ball in a tetherball game.
The sun is the pole
Gravity is the tether (rope) that attaches the ball to the pole
Inertia is the forward motion of the ball after it is hit.