※ 引述《mrchiucty (Eric)》之銘言：
: [單元] 重力場
: [來源] 101中山光電
: [題目] https://imgur.com/a/Tm3f9
: [想法] https://imgur.com/a/859VE
: 要球距離球心d的一點質量m所受的重力，為什麼不是d^3/R2^3?
ρ = M(3/4)/[π(R_2^3 - R_1^3)]
d
F = [(m G ρ)/(d^2)] * ∫4πr^2 dr
R_1
= m M G (3/4)/{[π(R_2^3 - R_1^3)]d^2} * (4π/3)[d^3 - R_1^3]
= m M G [d^3 - R_1^3] / {[(R_2^3 - R_1^3)]d^2}