万有引力定律 地球可视为球体，自转周期为t，在两极测得一物体重为p，在赤道，测得同一物体重为0.9p，求地球的平均密度 “万有引力与重力的差”提供向心力：p=gmm/r^2（在两极）p-0.9p=m(2π/t)^2*r（在赤道）由上两式得：m/r^3=40π^2/(g*t^2)ρ=m/v=m/(4πr^3/3)=(m/r^3)*(3/4π)=(40π^2/(g*t^2))*(3/4π)=(30π)/(gt^2) 万有引力与重力的差等于向心力：在两极时：p=gmm/r^2在赤道时：p-0.9p=m(2π/t)^2*r由上两式得：m/r^3=40π^2/(g*t^2)则地球密度为：ρ=m/v=m/(4/3πr^3)=(m/r^3)*(3/4π)=[40π^2/(g*t^2)]*(3/4π)=30π/(gt^2)
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