Download CHPT 1 – Section 2 Notes

CHPT 1 – Section 2 Notes
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Gravity & Orbital Motion of the Earth/Moon System
I.
Astronomy --
the study of the universe and the objects in it,
including stars, planets, and galaxies.
A. “Astro” comes from the Greek word for star
B. “Nomy” comes from the Greek word for law
II. Gravity -- the force that attracts all objects to each other
A. Force – push or pull
B. Weight is the measure of the force of gravity

weight does NOT stay the same on other planets
B. Law of Universal Gravity – everything in the universe attracts
everything else
C.
Strength of gravity depends on 2 factors:
1. Mass – amount of matter in an object (Does NOT change on other
planets)

Large mass means large gravity

Smaller mass means weaker gravity
2. Distance – Increased distance means weaker gravity

The closer an object is, the stronger its gravity is
felt

The farther an object is, the less its gravity is felt
III. Inertia -- is the tendency of an object to resist a change in motion

Newton’s 1st Law of Motion: an object at rest will stay at
rest, & an object in motion will stay in motion until another
force acts on it.
IV. Orbital Motion:
The moon’s motion would normally be a straight line,
but since Earth’s gravity pulls
it towards the Earth, the path
will curve into an orbit around
it.
A. Inertia & gravity combine
to keep the Earth in
orbit around the sun
B. Inertia & gravity combine
to keep the Moon in orbit around Earth