Physics > Gravitation > 2.0 Variation of acceleration due to gravity

  Gravitation
    1.0 Newton's law of gravitation
    2.0 Variation of acceleration due to gravity
    3.0 Gravitational field
    4.0 Gravitational potential
    5.0 Gravitational potential energy
    6.0 Satellites
    7.0 Kepler's law of planetary motion
    8.0 Problem solving technique

2.4 Variation of acceleration due to gravity $(g)$ due to rotation of earth


Consider a body at a point with latitude on the surface of the earth.

Let,

$R$: Radius of the earth
$\omega $: Angular velocity of the earth about its own axis



Acceleration vector



$$\overrightarrow g ' = \overrightarrow g + {\omega ^2}\overrightarrow r $$ $$\left| {\overrightarrow g '} \right| = \sqrt {{g^2} + {r^2}{\omega ^4} + 2g{\omega ^2}r\cos \left( {\pi - \theta } \right)} $$ $$\left| {\overrightarrow g '} \right| = \sqrt {{g^2} + {r^2}{\omega ^4} - 2g{\omega ^2}r\cos \theta } $$
As, $\left( {\omega < < 1} \right)$. So, $\left( {{\omega ^2} \approx 0} \right)$.

So, $$g' = {\left( {{g^2} - 2gr{\omega ^2}\cos \theta } \right)^{\frac{1}{2}}}$$
Also, $$r = R\cos \theta $$ So, $$g' = {\left( {{g^2} - 2gR{\omega ^2}{{\cos }^2}\theta } \right)^{\frac{1}{2}}}$$$$g' = g{\left( {1 - \frac{{2R{\omega ^2}{{\cos }^2}\theta }}{g}} \right)^{\frac{1}{2}}}$$ Using binomial expansion, $$g' \approx g\left( {1 - \frac{{R{\omega ^2}{{\cos }^2}\theta }}{g}} \right)$$$$g' = g - R{\omega ^2}{\cos ^2}\theta $$
  • At the equator $\theta = 0^\circ $
    $$g' = g - R{\omega ^2}$$
  • At the pole $\theta = 90^\circ $
    $$g' = g$$
The value of acceleration due to gravity is minimum at the equator and maximum at the poles. Thus $g$ increases as we move from equator to the pole.
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