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6/27/2017
Ch 7 Gravitation Review Sheet
The test is 35 MC questions (35 points).
One 5 point problem.
One bonus question (analytical regarding Kepler’s Laws.)
Total points = 40.
The following list highlights the concepts covered on the test
Apparent Motions in the night sky. Planets are “wanderers” that exhibit retrograde
motion. This distinguishes the planets from the stars.
Models to explain the apparent motions:
Ptolemy: Had a geocentric (earth-centered) model with planets orbiting the earth in
epicycles.
Copernicus: Had a Heliocentric (sun-centered) model with planets orbiting the sun in
circular orbits.
Kepler: Developed three laws describing planetary motion using data from Tycho Brahe.
His model has planets orbiting the sun in elliptical orbits.
You should know his three laws, and be able to use the equation
developed from the Law of Harmony
What force drives the Kepler Model?
Newton’s Universal Law of Gravitation
You should know the equation. Be able to describe the relationships in words, with
graphs, with calculations, and applications.
For orbiting objects (moons, satellites, comets) that have a change in (mass, radius, or
velocity) you should be able to tell how (Fg, T, vel, “g”) are affected. This could be in
words, with calculations, or with graphs.
The concept of “weightless” occurs when an object is in freefall. That means that gravity
is the only force. “Weightless” does not mean that gravity stopped acting.
Know the difference between mass and gravitational force (weight).
The universal gravitational constant is G. You should know its value, how it was
determined, and who found it.
Fg in th\e gravitational equation is the value for both earth on moon, moon on earth (etc).
These are third law partner forces. So, third law questions are fair game.
Circular motion concepts that apply to planetary motion:
- velocity is a tangent to the orbital path
- the speed is constant, the velocity is not (i.e. changing directions)
- the orbiting object accelerates
- orbiting objects are “falling” towards the center
- the acceleration and net force are toward the center
Gravitational field strength (“g”) vs. acceleration caused by gravity (“g”):
Define field strength
Distinguish between field strength and weight
Calculate field strength for a position in space above planet surface
Calculate field strength for a planet’s surface given mass and radius
As a planet moves closer to the sun, the (a) _______________ will
(b) _______________ (increase, decrease, not change).
a. gravitational force
b. mass
c. tangential velocity
d. gravitational field strength
A satellite doubles its distance from the center of the earth. This causes
(a) ____________ to (b) _________________ (increase, decrease, not change).
a. period
b. gravitational field strength
c. tangential velocity
d. mass
e. gravitational force
A satellite doubles its mass. This causes (a) _____________ to
(b) ________________ (increase, decrease, not change).
a. period
b. gravitational force
c. tangential velocity
d. orbital radius
e. gravitational field strength
A fat astronaut and a skinny astronaut orbit in the space shuttle with the same (select all
that apply)
a. mass
b. period
c. orbital velocity
d. gravitational force
e. gravitational field strength
f. radius