Edmond Halley 16561742

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Christopher Wren (1632-1723)
Edmond Halley (1656-1742)
Robert Hooke (1635-1703)
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Isaac Newton 1642 - 1727 If I have been able
to see further, it was only because I stood on
the shoulders of giants.                      
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Picture the London gentleman-intellectuals
dining group (Events in history? England was
becoming a world power) Halley (sea captain, what
else?) Hooke (discovered body is made of little
living cells, physics of springs) Wren
(architect, astronomer) The Bet Hooke said he
knew the answer but wouldnt tell! Yeah,
right. Note how Halley asked Newton the
question Would the orbit be an ellipse if
1/r2 law? Seems to me Halley already had a good
idea. Newton said, yes, he had solved it
already. Ellipse matches observed orbits of
planets!
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Isaac Newton 1642 - 1727 If I have been able
to see further, it was only because I stood on
the shoulders of giants. FORCE OF GRAVITY F
G ? M1 ? M2 / r2                                  
               
G x Mass1 x Mass2 (distance)2
Force
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Newtons discoveries Law of gravity F
Gm1m2/r2 Activity on mass and inverse-square
effect of gravity formula Concept of inertia
(also called momentum) Every mass wants to
keep moving at a constant speed in constant
direction, unless there is a force on it.
Fma Symmetry Equal and opposite
forces Same laws governing astronomical motion
(e.g. planets) as motion on Earth (e.g.
apples falling). WEIGHT vs. MASS Bryson got it
wrong!
weight of the Earth
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Measuring Earth Why Navigation! Remember what
England was busy doing then. Measure of Earth by
Norwood How? Seeing how far away the Sun
direction shifts from place to place.
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• How long is 1 degree in miles (or km).
• Hey its exactly 60 Nautical Miles. Mere
  coincidence or . . .
• Measuring Earth flattening (fatter around its
  equator)
• Cassini error, later fixed by another French
  team (who aced out poor Bouguer)
• Who was Cassini?
• Activity
• Why is Earth fatter around the equator?
• (Recall Newtons idea about inertia.)
• 2. If Earth stops spinning suddenly, will we
  all fly off it? VOTE

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Getting mass of Earth Use orbits of planets
Moon (Newton did it 100 years earlier) or
Scotch mountain, or Cavendishs approach of
measuring G in lab. Getting size of solar
system Triangulation -- Something our
brains do all the time! Stories of
Venus transit Mason and Dixon Importance in US
history. Most of the measuring in this chapter
was in the 1700s, about 100 years after the
Halley, Wren, Hooke, Newton crowd. What was
going on in the world around the late 1700s?