Description:
The Earth is rotating, and therefore it is an oblate spheroid. The vector representing true gravity can be decomposed in a component perpendicular to the surface and a component perpendicular to the Earth's axis. The component of true gravity that acts perpendicular to the Earth's axis provides the force that keeps objects at the same latitude. In the hypothetical case of a perfectly spherical rotating celestial body, all water and air would gather at the equator. Each component of true gravity has a different effect: the effect of the perpendicular to the surface component is that objects remain tightly on Earth; the result of the perpendicular-to-the-Earth's-axis-component is that all objects that are stationary with respect to the Earth remain on the same latitude. The arrow on the outside shows the local direction of a plumb line; the line that is perpendicular to the surface. Created: august 10, 2005