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Unformatted text preview: 1 Lecture 21 Gravity Weight Gravitational field strength Work by gravity/gravitational potential energy Escape velocity 2 2 2 1 r M GM F = Gravity is the force between two masses. Gravity is a long range or field force. No contact is needed between the bodies. The force of gravity is always attractive! r is the distance between the two masses M 1 and M 2 and G = 6.67 1011 Nm 2 /kg 2 . M 2 r M 1 F 21 F 12 . 12 21 F F = 3 Where the unit vector points from the source of the gravitational field (location of M 1 ) to the field point (location of M 2 ). r F 2 2 1 r M GM = In vector form 4 Example: Three masses are arranged as shown. What is the force of mass 1 on mass 3? M 3 M 2 M 1 b a 13 r y x r F 2 3 1 13 r M GM = ( 29 ( 29 y x y x r r r y x y x r cos sin 2 2 1 3 1 3 + = + + = = + = + = b a a b a b y y x x 5 Example Continued ( 29 + + + + = y x F 2 2 2 2 2 2 3 1 13 b a a b a b b a M GM 6 Example: Three masses are arranged as shown. Example: Three masses are arranged as shown....
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 Spring '11
 Staff
 Energy, Force, Gravity, Mass, Potential Energy, Work

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