RANDY L. PHELPS
This is the module for "Gravity"
1. For this module, please look through the "lecture" notes
for "Gravity".
These notes contain the material, in condensed form, that I will expect you to become
familiar with. I am sure you will have questions about the material, especially
since it is presented in the form of lecture notes. To help you expand upon the
material, and fill in some blanks, check out the following web sites:
2. Do the following interactive web assignment: Newton's Cannon
Upon completion of
this web assignment, you should be comfortable with the following material:
- Kepler's 3 Laws of Planetary Motion: What
they are and what can one learn from them. One should be especially familiar with
the 3rd law in its three forms, and know why each is important. How can one use
Kepler's 3rd law to determine the mass of an object.
- Conic Sections: What are the various types
of conic sections, and what are their properties. What are the semi-major axis and
eccentricity, and how are they related to properties of conic sections.
- Newton's 3 Laws of Motion: What they are.
In particular, what does the 2nd law say about the motion of objects.
- Newton's Law of Gravity: What quantities go
into the description of gravity, according to Newton. If one changes one of the
quantities, how does the force of gravity change.
- Orbital velocities: What is circular
velocity, and how does it change as one changes various quantities that determine it.
What is escape velocity and hoe it is determined. How escape velocity
compares with the circular velocity. What are kinetic and potential energy, and how
they relate to total energy.
Upon completion of
this assignment, you should be able to answer these, and similar, questions
General Concepts
- What are Newton's 3
Laws of Motion?
- What are Kepler's 3 Laws of
Planetary Motion?
- What is the eccentricity of a
circle, a parabola and a hyperbola?
- Which planet would orbit the Sun
with a longer period, one with a semimajor axis of 2.5 AU, or one with a semimajor axis of
3.5 AU?
- If a planet's orbit has a
semimajor axis of 5 AU, and an eccentricity of 0, what are the perihelion and aphelion
distances of the planet from the Sun?
- Is an obect in a circular orbit,
with a constant velocity, accelerating? Why or why not?
- If an artificial satellite is
given just less than the circular velocity, what type of orbit, if any, will it attain?
- If an artificial satellite is
given the escape velocity, what type of orbit will it attain?
- If an artificial satellite is
given greater than the escape velocity, what type of orbit will it attain?
Applications
Describe a set of observations that would
allow you to determine the mass of the Sun.
Describe a set of observations that would allow you to determine the mass of Mercury,
which has no moons.
Describe a set of observations that would allow you to determine the mass of Mars, which
has two moons (Deimos and Phobos).
Describe a set of observations that would allow you to determine the mass of a star
which has a small companion orbiting it.
Two objects with equal mass are separated by 4 feet. One object is moved to a distance
of 8 feet. How does the force of gravity between them change?
Two objects with equal mass are separated by 2 astronomical units. One object is moved
to a distance of 6 astronomical units. How does the force of gravity between them change?
Two objects with equal mass are separated by 2 feet. One object is replaced by another
with 3 times the mass. How does the force of gravity between them change?
The
These questions, and similar ones, will form the basis of the exam
material for this section of the course. If you have problems with the material,
please see me during my office hours. If you are unable to answer some of the questions, I
will help you before the date specified on the syllabus, provided you show me the results
of your inquiry into the material.
That is, you must provide me the answers you
we able to obtain for all questions, including your attempts at problem questions, before
I will help you with any of them!
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