Homework Assignment (due on Tuesday)  JO
1) Why did Plato propose that all heavenly motion was uniform and circular?
Because the most perfect geometrical form was the sphere and therefore the most perfect
heavens must be made of up spheres rotating at constant rates and carrying objects
around in circles.
2) Why did Copernicus need to include small epicycles in this model?
Copernicus placed the sun at the center of the system. But, he continued to use perfect
circles for the planets orbits.
Since the orbits are not perfect circles (they are ellipses), planets would fall behind of his
calculated values. So he had to reintroduce epicycles to account for the differences.
3) What are Kelper's 3 laws of motion?
I. The orbits of the planets are ellipses with the sun at one focus.
II. A line from a planet to the sun sweeps over equal areas in equal intervals of time.
III. A planet’s orbital period squared is proportional to its average distance from the sun
cubed:
P
2
yr
= a
3
AU
4) If a planet has an average distance from the Sun of 4 AU, what is its orbital period?
4
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document
This is the end of the preview.
Sign up
to
access the rest of the document.
 Spring '09
 Smith
 Work, General Relativity, Gravitational forces, circular orbit, Copernicus, perfect geometrical form

Click to edit the document details