86.1 The gravitational force relative to the elevator ∑F,=T-mg-ma=0 T=mg+ma @If the cable breaks, a n T=0 The fish is weightless 86.2 Gravitational force of a uniform sphere on a particle 1. Shell theorem #1 A uniformly dense spherical shell attracts an external particle as if all the mass of the shell were concentrated at its center 2. Shell theorem #2 a uniformly dense spherical shell exerts no gravitational force on a particle located anywhere inside it 66 ③If the cable breaks, a= -g ②relative to the elevator T mg ma F T mg ma y = + ∑ = − − = 0 a r T r mg r ma r T = 0 The fish is weightless. §6.1 The gravitational force §6.2 Gravitational force of a uniform sphere on a particle 1. Shell theorem #1 A uniformly dense spherical shell attracts an external particle as if all the mass of the shell were concentrated at its center. 2. Shell theorem #2 A uniformly dense spherical shell exerts no gravitational force on a particle located anywhere inside it