Chapter 9: Gravity

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Chapter 9 Gravity
Gravity is the force most familiar to us, and
yet, is the least understood of all the
fundamental forces of nature.
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Four Fundamental Forces of Nature

1. Gravity
2. Electromagnetism
3. Strong Nuclear Force (This holds atomic nuclei
   together)
4. Weak Nuclear Force (Allows for radioactive decay)

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Keplers Three Laws of Planetary Motion
Go Columbia!!
Johannes Kepler (1571-1630)
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First Law
Each planet moves in an elliptical orbit with the
Sun at one focus.
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An Ellipse
Foci
r1r2 constant
a
Minor Axis
r2
r1
Semi-major Axis (a)
Major Axis
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Orbiting planet
Sun at one focus
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The Second Law
The line from the sun to any planet sweeps out
equal areas in equal times.
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Orbiting planet
A
Sun
A
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The Third Law
The square of the orbital period is proportional
to the cube of the semi-major axis
For a circular orbit, the semi-major axis is the
radius
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Newtons Law of Universal Gravitation
Every body in the universe exerts a force on
every other body which is proportional to the
product of their masses and inversely
proportional to the square of the distance
between them
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R
M1
M2
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The Tides
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Einsteins Theory of Gravity
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a g
a g/2
a 0
a g/2
a g