Gravity

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Gravity

• Ch. 12

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Newtons General Law of Gravitation(Ch. 12 Sect
12-1)

• Newtons General Law of Gravitation applied to
  the earth (ME)
• The force of gravity between two any points

G 6.67 10-11 N.m2/kg2 - the universal
gravitation constant
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Examples

• 1. The force of gravity between 2 people (m150
  kg, m2100 kg) 2 m apart
• 2. The force of gravity between Earth and Moon

very small
significant
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Force of gravity

• Significant only when large masses (like
  planets) are involved

• Is directed along a line connecting the masses
  (masses are treated as point objects)
• Vector (if many objects are involved the vector
  sum of all forces exerted on a particular object
  must be found)

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Example 12-1p. 350How Much Force Is With You?
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Force of gravity

• Force between a person and the Earth

Gravity on other planets can be found in the same
way
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Force of gravity

• What is the acceleration due to gravity in the
  mountains?

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The Acceleration Due to Gravity at a Height h
Above the Earths Surface
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Keplers Laws

• Keplers first law Planets follow elliptical
  orbits, with the Sun at one focus of the ellipse.

• Keplers second law As a planet moves in its
  orbit, it sweeps out an equal amount of area in
  an equal amount of time.

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Keplers Third Law

• The period, T, of a planet increases as its mean
  distance from the Sun, r, raised to the 3/2
  power. That is
• T (const) r 3/2

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Satellite motion

• constant speed

Derivation on the board!