- #1

AntiElephant

- 25

- 0

I want to focus on a point (a "piece" of Earth's matter) on the Earth's surface, along the equator, to understand why it bulges outwards. If the Earth was initially stationary and spherical, then the only force acting on this piece would be gravity [itex] F_{grav} [/itex]. As the Earth gradually begins to rotate a centrifugal force [itex] F_{centrif} [/itex] appears pointing in a direction outwards, opposite to the axis of rotation, a fictitious force as a result of being in a non-inertial frame of reference.

The total force on this piece would be [itex] F_{grav} - F_{centrif} [/itex]. If [itex] F_{centrif} <= F_{grav} [/itex] then surely the piece would still have a resulting force pointing towards the centre of the Earth and the Earth would remain spherical? If/once [itex] F_{centrif} > F_{grav} [/itex] then the piece would "fly" off from the Earth (in a stationary frame, this would be a result of inertia). Have I looked at this too simplistically? How, then is it that the Earth bulges and instead isn't at either of the extremes - either spherical or stuff "flying" off as a result of inertia?