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73 63, galileo measur us newton basi law motion
75 45, galileo experi bodi roll slope act same forc weight effect
+make constantli speed up
70 50, show real effect forc chang speed bodi set move previous th
+ought
75 50, meant bodi act forc keep move straight line same speed
65 45, idea first state explicitli newton principia mathematica pu
+blish 1687 known newton first law
75 50, happen bodi forc act given newton second law