Chapter One, Section Two: Gravity and Motion

Essential Question: What effects are caused by the motion of the Earth and moon?

Objectives: Explain what determines the strength of the force of gravity between two objects. Explain what two factors combine to keep the moon and Earth in orbit.

Force- push or pull Gravity A. gravity- force that attracts all objects toward each other B. Newton’s law of universal gravitation states that every object in the universe attracts every other object.

C. Strength of force of gravity between two objects depends on: mass of objects and distance between them D. Gravity, Mass, and Weight 1. mass- amount of matter in an object 2. Earth exerts a force on the moon that keeps it in orbit

3. weight- force of gravity on an object 4 3. weight- force of gravity on an object 4. weight can change, mass can not 5. Ex. On the moon you would weigh about 1/6 th of what you weigh on Earth

E. Gravity and Distance 1. strength of gravity is affected by distance between 2 objects as well as their masses II. Inertia and Orbital Motion A. Inertia 1. inertia- tendency of an object to resist a change in motion

2. Newtons 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

B. Orbital Motion 1. Newton concluded: inertia and gravity work together to keep Earth in orbit around the sun and the moon in orbit around the Earth