phy53 lect			dr. brown		28 october 2010

exam remarks

range 9-107  encouragement for those who got lower grade on the exam...  consider how you're studying

covered as example short answer #3 -- use as diagnostic about your approach to the problem

done with mechanics -- heading to gravitation, fluids, waves ...

Galileo -- using pulse observed pendulum had constant period for given length
        -- got caught up in philosophical debate Capernicous (sp), Ptolemy 
	a=g

Newton  --  F = ma = mg ,  F_{ij} = -F{ji}
	--  apple 
	F proportional to product of masses and has some distance component
	reasoning -- gravitation "stuff" passes through sphere ... geometry suggests the functional form is inverse 	 square.. so, 

   		F = \frac{G m_1 m_2}{r^2}

how can Newton test this?  take ratio of accelerations of apple and moon

parallax used to find distance to moon  -- with good value for distance to moon IT CHECKED!

First law of Nature -- Newton's law of gravitation -- properly "coordinitized"  as vector equation

derived Keplers 3rd Law from newton's  radius of orbit cubed is proportional to square of period

kepler's 1st = planets form elliptical orbits about the sun

kepler's 2nd = planets sweep out equal areas in equal times = angular momentum over 2m ; note radial force exerts zero torque and therefore angular momentum is constant

lots of evidence from Kepler for validity of Newtons law of gravitation

We still need to know G = 6.67 x 10^{-11} ! note 'tis SMALL 
[Cavandish]