\(g =\frac{ GM }{ r ^2}\)
I = distance from center of earth
\(\Rightarrow g ( h )=\frac{ GM }{( R + h )^2} \Rightarrow g ( h )=\frac{ GM }{ R ^2\left(1+\frac{ h }{ R }\right)^2}\)
\(\Rightarrow g ( h )=\frac{ GM }{ R ^2}\left(1+\frac{ h }{ R }\right)^{-2}\)
\(\text { If } h \ll R ,\left(1+\frac{ h }{ R }\right)^{-2} \approx 1-\frac{2 h }{ R }\)
\(\Rightarrow g ( h )=\frac{ GM }{ R ^2}\left(1-\frac{2 h }{ R }\right)\)
\(\Rightarrow g ( h )= g _{\text {surface }}\left(1-\frac{2 h }{ R }\right), \frac{ GM }{ R ^2}= g _{\text {surface }}\)
($M$ એ પૃથ્વીનું દળ, $R$ એ પૃથ્વીની ત્રિજ્યા, $G$ ગુરુત્વાકર્ષી અચળાંક છે.)