※ 引述《mrchiucty (Eric)》之铭言：
: [单元] 重力场
: [来源] 101中山光电
: [题目] https://imgur.com/a/Tm3f9
: [想法] https://imgur.com/a/859VE
: 要球距离球心d的一点质量m所受的重力，为什么不是d^3/R2^3?
ρ = M(3/4)/[π(R_2^3 - R_1^3)]
d
4πd^2 a = G ρ4π∫r^2 dr
R_1
= (4/3)πGρ[d^3 - R_1^3]/(d^2)
=> a = M G [d^3 - R_1^3] / {(R_2^3 - R_1^3) d^2}
=> F = ma = m M G [d^3 - R_1^3] / {(R_2^3 - R_1^3) d^2}