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]