lec25_review30 - R3-1Physics IReview 3Review Notes - Exam...

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Unformatted text preview: R3-1Physics IReview 3Review Notes - Exam 3Ch 12, 13, 15, 16, 17, 2126-2Equilibrium for Rigid ObjectsWhen dealing with objects that have finite size, we specify external forces and external torques. Equilibrium: constant ()constant any coordinate systemany axi()so,sextextPLF====Center of GravityWhen calculating torque due to gravity we can use the center-of-mass, renamed center-of-gravity.dm=(M/L)dx2()|What is the direction of||||222|()?extcmgravLextegravLextxtxgMdxg dmdxLxgMddxLxxgMLgMLMLMgg========R3-4Newtons Law ofUniversal GravitationrrmmGF221=The meaning of each term:F:Gravitational force on object 1 from object 2.G:Universal gravitational constant = 6.673 x1011N m2/kg2.1m:Mass of object 1.2m:Mass of object 2.2r:Center distance from object 1 to object 2, squared.r:Unit vector from object 1 to object 2.R3-5If Gravity Varies As 1/r2,Where Does g = 9.8 m/s2Fit In?Consider the force on an object near the surface of the earth.(Assume the earth is a sphere and ignore rotation effects.)R = radius of the earth.M = mass of the earth.m = mass of the object.gmrRMGmrRMmGF22===(What is the direction?)g = 9.8 m/s2only seems constant because we dont go very farfrom the surface of the earth.Gravity is aConservative ForceSince the force goes to zero at infinite distance, we set the gravitational potential energy to zero there also (it's the only unique point): 2( )( )( )( )gravgravgravRRgravRURUURF drFdrG mMG mMURdrrR -= -= += -= -Here the integral starts at R and goes to infinity so the dot product is always...
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lec25_review30 - R3-1Physics IReview 3Review Notes - Exam...

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