February 20, 2008 - WRITTEN HW DUE MONDAY LUNAR ECLIPSE...

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February 20, 2008 WRITTEN HW DUE MONDAY LUNAR ECLIPSE TONIGHT FROM 6:45 TO 10:09 How many planets have rings? o 4, Jupiter Neptune Saturn and Uranus o The gas giants have rings Rings are very different than moons o Not all the planets even have moons o Earth Mares Jupiter Saturn Uranus and Neptune have moons Suppose earth were moved to one-third of its current distance from the sun. What would happen to the gravitational force between Earth and Sun. o Mathematical approach: F g = G [(M 1 M 2 )/ d^2] F new /F old = {G [(M S M E )/ ((1/3d)^2)]}/{ G [(M S M E )/ d^2]} = 1/(1/9) = 9 (everything cancels out) Multiply both sides by F old => F new = 9F old F new is greater by 9 o Logical Way F = (GM 1 M 2 )/(d^2) d decreases by 3 d^2 decreases by 9 F increases by 9 Newton’s version of Kepler’s third law o Orbital period = totally distance/speed o Circular orbit P = 2pia/V circ r = a for circular orbits p^2 = (2pir)^2/(V circ )^2 p^2 = (4pi^2a^2)/(GM/a) p^2 = [4pi^2/GM]a^3 (something)a^2/(something/a) Bring the a up to the top
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