We discussed that value of gravitational field strength at
different locations on Earth Surface, at an altitude or at a depth are
different. Similarly value of g is also affected by other factors like shape of
Earth and rotational motion of Earth.
Effect on value of g
due to shape of Earth: In analysis of calculation of gravitational field
strength on surface we considered Earth as a solid sphere. But actually Earth
shape is ellipsoidal not exactly spherical due to which the results of
gravitational field strengths of a solid sphere are not appropriate to use. The
shape of Earth is flat at poles and having more curvature at equator due to
which gravitational field strength is slightly more at poles then equator. To
see the detailed understanding watch the video here: https://youtu.be/QnIH92fgmbw
Effect on value of g
due to rotational motion of Earth: Every object or a body placed on Earth
surface is in circular motion with centre located on the axis of rotation of
Earth. Thus due to the accelerated motion Earth surface is a non-inertial
reference frame and for analysis of dynamics of any object on Earth surface we
must use centrifugal force on the body in radial direction away from centre of
circular motion of the body. Due to this inertia force on body the effective
weight of body decreases.
Also at different locations on Earth surface the radius of
circles in which the bodies are moving are also different so centrifugal force
considered will also be different so variation in value of g will also be different.
See the video here for detailed understanding: https://youtu.be/lNJ2icc1fPk