6.1. Kepler’s Laws of Planetary Motion http://www.ck12.org
Summary
- Kepler’s First Law: The path of each planet around the sun is an ellipse with the sun at one focus.
- Kepler’s Second Law: Each planet moves such that an imaginary line drawn from the sun to the planet sweeps
out equal areas in equal periods of time. - Kepler’s Third Law: The ratio of the squares of the periods of any two planets revolving around the sun is
equal to the ratio of the cubes of their average distance from the sun.
Practice
Questions
The following is a video about Kepler’s three laws. Use this resource to answer the questions that follow.
http://www.youtube.com/watch?v=6TGCPXhMLtU
MEDIA
Click image to the left for use the URL below.
URL: http://www.ck12.org/flx/render/embeddedobject/62072- What is the shape of a planetary orbit?
- How are the areas swept out by the line able to be equal, when the line is much longer at some times than
others? - What is the T in Kepler’s Third Law? What is the r?
Review
Questions
- The average mean distance of the earth from the sun is 149.6× 106 km and the period of the earth is 1.0
year. The average mean distance of Saturn from the sun is 1427× 106 km. Using Kepler’s third law, calculate
the period of Saturn. - Which of the following is one of Kepler’s Laws of Planetary Motion?
(a) Planets move in elliptical orbits with the Sun at one focus.
(b) Gravitational force between two objects decreases as the distance squared.
(c) An object in motion remains in motion.
(d) Inner planets orbit in a different direction that outer ones. - If a planet’s orbital speed is 20 km/s when it’s at its average distance from the sun, which is most likely orbital
speed when it is nearest the sun?
(a) 10 km/s
(b) 15 km/s
(c) 20 km/s
(d) 25 km/s
- Kepler’s First Law:The path of each planet around the sun is an ellipse with the sun at one focus.
- Kepler’s Second Law: Each planet moves such that an imaginary line drawn from the sun to the planet
sweeps out equal areas in equal periods of time.