Figure 4. The shape of a sphere by pulling the mass of the earth close to the center of gravity. Blue arrows point from Earth’s surface toward its center. Their lengths represent local gravitational field strength. Gravity is strongest at the poles because they are closest to the center of mass. This difference is enhanced by the increasing density toward the center. Red arrows show the direction and magnitude of the centrifugal effect. On the equator, it is large and straight up. Near the poles, it is small and nearly horizontal. Vector addition of the blue and red arrows gives the net result of gravity plus centrifugal effect. This is shown by the green arrows. Rotation of the earth produces more centrifugal force at the equator, less as latitude increases, and zero at pole.