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Review Questions

Chapter 22, Part 2 – Planetary Motion

1.      Explain the contributions of each person:

a.       Copernicus – developed the heliocentric model of the solar system

b.      Tycho Brahe – made detailed observations of the sky pre-telescope days

c.       Kepler – developed 3 laws of planetary motion using Tycho’s notes

d.      Newton –  developed the universal laws of gravitation

e.       Ptolemy – developed the Geocentric model for the solar system.  It included epicycles and deferents

f.        Galileo – first to use a telescope to view the sky.  Observed many things, especially evidence for the heliocentric model of the solar system.

2.      Explain Kepler’s first two laws fully.  Make a diagram of each and label it.

1st Law – planets travel in elliptical orbits with the sun at one of the two foci.  The point nearest the sun is the perihelion, and farthest from the sun is the aphelion.

2nd Law – Equal Area Law.  Planets will sweep the same amount of area in the same amount of time.  Speed changes.

3.      What does Kepler’s third law of planetary motion state?

Known as the Harmonic Law.  The period of a planet squared = the distance of the planet from the sun cubed.  If you know one, you can figure out the other.

4.      If the distance to Planet X is 4,000 AU, which is the period?  Show all work!

P2 = D3 Therefore P2 = (4000)3 = 6.4 x 1010, so √6.4 x 1010 = 8 x 105

5.      Galileo proved that our solar system was not geometric.  What did he discover and how did he prove it?

Galileo observed Venus experiencing all the phases just like out moon.  If Geocentric system was correct the only phases we would observe of Venus are new and full.

6.      What does Issac Newton’s Universal Law of Gravitation state?

Two objects will exert a force upon each other.

7.      What happens to the force of gravity between the two objects if their distance increases?

Gravity will decrease.

8.      What happens to the force of gravity between the two objects if their size increases?

Remember it is not size BUT MASS AND DISTANCE!!!

9.      What is the difference between an ellipse and a circle?  Which is the shape that the planets follow in their orbits?

An ellipse has two foci, and a circle has one.  Planetary orbits are ellipses, that are almost circular in shape.  Therefore e = to almost 0.

10.  Draw a picture of Ptolemy’s vision of the solar system, and label it.

Remember to include deferent and epicycles.

11.  What is retrograde motion?

The looping motion that some of the planets appear to make in the sky over time, as they rise in the west and move eastward – occasionally looping towards the west again.

12.  Why did ancient peoples believe the Earth was the center of the universe?

It seemed obvious.  The sun and moon would rise and set daily with predictable changes in the cycle.  The stars seemed to move in fix pattern.  If the Earth was moving around the sun we should feel it, or fall off.