Smartphones and Gravitational Acceleration I: Overview

Geodesy is a very active and essential research discipline in geophysics but it is not a commonly studied subject at the secondary school or junior post-secondary levels. Far more frequently, gravity and gravitational acceleration are discussed, to some extent, in elementary kinematics or classical mechanics courses. This often takes the form of the force acting on a body or bodies due to gravity, or that the acceleration (a_grav) of a free-falling body is 9.8(1) m/s²—which implies the setting of the question is at Earth’s surface. While the latter is a reasonable and practical approximation, a_grav observed over the surface of Earth varies and is dependent on several factors. These are normally related to elevation and latitude variations caused by Earth’s rotation. Earth’s rotation contributes negatively to a_grav at the equator due to the centrifugal force outward and equatorial bulge, which makes the equatorial radius larger than the polar radius. Offsetting this partially is the positive contribution to a_grav at the equator caused by the equatorial bulge because of the extra mass comprising the bulge.