Reading assignment: Chapter 14.1-14.4

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Chapter 13
Reading assignment Chapter 14.1-14.4 Homework
(due Monday, Oct 31, 2005) Problems Q5, Q10,
1, 3, 7, 12, 20,
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Keplers laws about planetary motion These laws
hold true for any object in orbit

• Keplers first two laws (1609)
• Planets move in _____________ paths around the
  sun. The sun is in one of the focal points (foci)
  of the ellipse
• The radius vector drawn from the sun to a planet
  sweeps out equal areas in equal time intervals
  (Law of ____________).

Area S-A-B equals area S-D-C
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Keplers laws about planetary motion
Keplers third law (1619) III. The ____________
of the orbital period, T, of any planet is
proportional to the ____________ of the semimajor
axis of the elliptical orbit, a.
Thus, for any two planets
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Keplers laws about planetary motion
Most planets, except Mercury and ________, are on
almost a circular orbit
Earth Ratio of minor to major axis b/a
0.99986.
For planets around sun
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Black board example 14.3 The solar system
Inner planets
Further out Saturn, Uranus, Neptun, Pluto
Calculate the mass of the sun using the fact that
the period of the earths orbit is 3.157107 s
and its distance from the sun is 1.4961011 m.
If the Mars year is 1.88 earth years, what is
Mars distance from the sun
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All nine planets of the solar system
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Gravitational potential energy

• Notice the sign
• U 0 at infinity

• U will get smaller (more negative) as r gets
  ________.
• Falling down means losing ______ potential
  energy.
• Use only when _____ away from earth otherwise
  use approximation U mgh.

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Black board example 14.4
How is
related to U mgh?
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Black board example 14.5
The First Rocket Launch from Cape Canaveral
(NASA) July 1950
At Earths surface a projectile is launched
straight up at 10 km/s. To what height will it
rise? Ignore air resistance.