Astronomy
Chapter 4: 5-8 Homework
Homework
Scholars Online Astronomy - Chapter 4: 5-8: Kepler's Eclipses and Newton's Gravity
Homework
- Reading Preparation
- Key Formulae to Know
- WebLecture
- Study Activity
- Chat Preparation Activities
- Chapter Quiz
- Lab Work
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
- Section 5: Galileo's observations of the phases of Venus, the craters of the moon, sunspots, and the moons of Jupiter effectively contradicted Aristotelian assumptions of perfect, unchanging matter moving with uniform circular motion around the earth.
- Section 6: Newton provided a physical explanation for Kepler's observations in three laws of motion describing inertia, the relationship between force and acceleration (F = ma) and the interaction of forces (the equal and opposite force rule).
- Section 7: Newton's universal law of gravitation describes a fundamental property of matter: all matter attracts all other matter, with a force dependent on the mass of each object and the distance between them: F = GMm/r2.
- Section 8: Gravitational forces will distort objects that are not rigid solids by acting with different amounts of force on the near and far sections of the object. This is how the moon causes tides in earth's oceans, and how galaxies distort one another.
Key Formulae to Know
- Newton's First Law of Motion: The definition of inertia
Objects do not change their state of motion (direction and velocity) unless acted on by an outside force.
- Newton's Second Law of Motion: The definition of force
Force = mass * acceleration
- Newton's Third Law of Motion: The principle of action and reaction
A force exerted by an object will give rise to an equal and opposite force exerted on the object.
- Kepler's Law
Newtonian form, all situations, period in seconds, distances in meters, masses in kg (to match units of G);
- Newton's law of gravity:
- Escape velocity:
Web Lecture
Read the following weblecture before chat: Aristotle, Ptolemy, Copernicus, Brahe, Kepler, Galileo, Newton: steps to planetary theory
Study Activity
Stellarium: Open Stellarium, set the time to about 7pm (19:00 hours) and turn off the atmosphere AND HORIZON. Find Jupiter (t should be above the SE-S horizon. Select it and zoom way into it, until you can see Ganymede, Callisto, Europa and (depending on exactly when you look) Io and Althea. Your field of view should be around 0.170°. Center Jupiter in the Stellarium window and double-click on it so that the red "selected" bars show.
In the steps below, make sure that you have double-clicked on Jupiter before advancing the time each time, so that it remains centered in your display.
- Now advance the clock one hour at a time to midnight. What happens to Jupiter and the moons? Which direction is Io moving? Which direction is Europa moving? Which direction is Callisto moving?
- Advance the clock to October 24, 2021 at midnight. Where are the moons now?
- Play with the time (forward and backward) to get a sense for the motion of the moons. Which moon is furthest from Jupiter? Which is closest?
- If you have time, see if you can figure out how long it takes Io, Europa, and Callisto to make a revolution (one complete orbit) of Jupiter.
UNL Tools Exercises
- Interactives:
- Use the Kepler's Laws module and its interactive task to explore Kepler's Three Laws.
- ClassAction:
- Study the concepts of gravity and any questions that you skipped in the Renaissance astronomy module.
- NAAP Labs:
- In Planetary Orbits, read about Kepler's Laws and Newton's Laws, then use the Planetary Orbit simulator to demonstrate how each of Kepler's laws works.
- For each of Kepler's laws: How does the rate of the planet in its orbit change when it is at aphelion? at perihelion? What happens if you increase the eccentricity of the planet's orbit?
Optional websites: Planetary Motion by Heather Welch. Use the Javascript version. Turn on "Predict Orbit when dragging." Then follow the directions to place your planet anywhere on the screen and then give it an initial velocity (speed and direction).
- Try to put the planet in a stable orbit (one where the ellipse or circle repeats itself).
- Try to put your planet in a parabolic orbit (extreme ellipse), and note the behavior when the planet is at perihelion and aphelion.
- Try to put your planet in a hyperbolic orbit. What happens to the planet?
Chat Preparation Activities
- Essay question: The Moodle forum for the session will assign a specific study question for you to prepare for chat. You need to read this question and post your answer before chat starts for this session.
- Go over the list of Key Words and Key Ideas at the end of the chapter. If you don't remember the definition of the key word, review its use (the page number on which it is explained is given).
- Read through the Review Questions and be prepared to discuss them in class. If any of them confuses you, ask about it!
- Mastery Exercise: The Moodle Mastery exercise for the chapter will contain sections related to our chat topic. Try to complete these before the chat starts, so that you can ask questions.
Chapter Quiz
- Required: Complete the Mastery exercise with a passing score of 85% or better.
- Go to the Moodle and take the quiz for this chat session to see how much you already know about astronomy!
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.
- Lab instructions:Mass of Jupiter
© 2005 - 2025 This course is offered through Scholars Online, a non-profit organization supporting classical Christian education through online courses. Permission to copy course content (lessons and labs) for personal study is granted to students currently or formerly enrolled in the course through Scholars Online. Reproduction for any other purpose, without the express written consent of the author, is prohibited.