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Chapter 1
Kepler’s Laws
Charles Hakes
Fort Lewis College
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Outline
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Logistics
Lab notes
Review
Kepler’s Laws
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Fort Lewis College
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Logistics
• Read about Newton (1.4).
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Fort Lewis College
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Lab notes
• Sunset Part 2
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Due ASAP
Important - Attach part 1!
update sketch if necessary
sketch both sunsets on the same plot
• Do Kepler small group for Friday.
• Due Friday at 5:30 P.M.
• In box outside room 671.
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Fort Lewis College
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I read the section on Kepler’s laws.
A) True
Charles Hakes
Fort Lewis College
B) False
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Planetary orbits are
A) Circular.
B) Parabolic.
C) Elliptical.
D) Hyperbolic.
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Fort Lewis College
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Planetary orbits are
A) Circular.
B) Parabolic.
C) Elliptical.
D) Hyperbolic.
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Fort Lewis College
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Two planets have orbits with the same
periods. Which is true?
A) Their velocities must be the same.
B) They must have the same eccentricity.
C) They must have the same semi-major axis.
D) Their orbits must be identical.
Charles Hakes
Fort Lewis College
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Two planets have orbits with the same
periods. Which is true?
A) Their velocities must be the same.
B) They must have the same eccentricity.
C) They must have the same semi-major axis.
D) Their orbits must be identical.
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Fort Lewis College
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Figure 1.15
Johannes Kepler (1571-1630)
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Fort Lewis College
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Kepler Overview
• Theoretician
• Used observations of Tycho Brahe
• Wanted a unifying principle to explain the motions
of the planets without epicycles.
• Took ~29 years, but he did it.
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Fort Lewis College
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Figure 1.16
Tycho Brahe
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Fort Lewis College
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Kepler’s “Laws”
• http://faculty.fortlewis.edu/hakes_c/
• Allow pop-up windows!
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Fort Lewis College
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Kepler’s “Laws”
• That “shape” law
• Orbits are elliptical, with the Sun at one focus.
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Fort Lewis College
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Kepler’s “Laws”
• That “shape” law
• Orbits are elliptical, with the Sun at one focus.
• That “speed” law
• (A line between the Sun and a)Planet sweeps
out (in the ellipse) equal areas in equal times.
Charles Hakes
Fort Lewis College
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Kepler’s “Laws”
• That “shape” law
• Orbits are elliptical, with the Sun at one focus.
• That “speed” law
• (A line between the Sun and a)Planet sweeps
out equal areas (of the ellipse) in equal times.
• That “math” law
P2 (years) = a3 (astronomical units)
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Fort Lewis College
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A planet orbit could be circular.
A) True
B) False
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Fort Lewis College
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A planet orbit could be circular.
A) True
B) False
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Fort Lewis College
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Two planets have orbits with the same
sized semi-major axis. Which is true?
A) The planet with the most eccentric orbit moves
faster all the time.
B) The planet with the most eccentric orbit moves
faster some of the time.
C) The planet with the most eccentric orbit never
moves faster.
D) Not enough information to answer.
Charles Hakes
Fort Lewis College
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Two planets have orbits with the same
sized semi-major axis. Which is true?
A) The planet with the most eccentric orbit moves
faster all the time.
B) The planet with the most eccentric orbit moves
faster some of the time.
C) The planet with the most eccentric orbit never
moves faster.
D) Not enough information to answer.
Charles Hakes
Fort Lewis College
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Assume a planet orbits exactly twice as
far from the Sun as the Earth does.
A) It’s period is 2 years exactly.
B) It’s period is between 2 and 3 years
C) It’s period is between 3 and 4 years
D) It’s period is 4 years exactly.
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Fort Lewis College
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Assume a planet orbits exactly twice as
far from the Sun as the Earth does.
A) It’s period is 2 years exactly.
B) It’s period is between 2 and 3 years
C) It’s period is between 3 and 4 years
D) It’s period is 4 years exactly.
Charles Hakes
Fort Lewis College
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Three Minute Paper
• Write 1-3 sentences.
• What was the most important thing
you learned today?
• What questions do you still have
about today’s topics?
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Fort Lewis College
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Three Minute Paper
• Answer this question (without
discussion):
• What is the air-speed velocity of an
unladen swallow?
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Fort Lewis College
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