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Chapter 4: 5-8 Homework

Course Materials are always under revision! Weblecture content may change anytime prior to two weeks before scheduled chat session for content.

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Scholars Online Astronomy - Chapter 4: 5-8: Kepler's Elipses and Newton's Gravity


Reading Preparation

Reading: Astronomy, Chapter 4: Gravitation and the Motions of the Planets, sections 5-8

Study Notes: notes on your assigned reading from the text

Key Formulae to Know

Kepler's Third Law

  • Simple form for planets orbiting the sun, period in Earth years and distances in astronomical units (AU): P 2   =   a 3
  • Newtonian form, all situations, period in seconds, distances in meters, masses in kg (to match units of G); P 2   =   4 π 2 G ( m 1 + m 2 )     a 3

Newton's law of gravity: F   =   G   ( m 1 m 2 r 2   )

Escape velocity:   v   =   2 GM R

Web Lecture

Read the following weblecture before chat: Aristotle, Ptolemy, Copernicus, Brahe, Kepler, Galileo, Newton: steps to planetary theory

Study Activity

Your Planetarium Program: Center the planetarium on Jupiter and set it to display the locations of the four Galilean moons at 9pm for any night in October 2018. "Observe" their motions by advancing the planetarium one day at a time for at least five days. Draw a diagram of the position of each moon each day relative to Jupiter. Can you determine the periods of the moons from your observations? Can you see all four moons for each observation?

Optional websites: Planetary Motion by Heather Welch.

    Follow the directions to place your planet anywhere on the screen and then give it an intial velocity (speed and direction).

  • Try to put the planet in a stable orbit (one where the ellipse or circl repeats itself).
  • Try to put your planet in a parabolic orbit (extreme ellipse), and note the behavior when the planet is at perhelion and aphelion.
  • Try to put your planet in a hyperbolic orbit. What happens to the planet?

Chat Preparation Activities

Chapter Quiz

Lab Work

Read through the lab for this week; bring questions to chat on any aspect of the lab, whether you intend not perform it or not. If you decide to perform the lab, be sure to submit your report by the posted due date.