Rotating-frame derivative formula Created 2026-09-29 Updated 2026-10-05
If a frame rotates with angular velocity relative to an inertial frame, the derivatives of any vector satisfy
Applying this formula twice to a position gives the Coriolis acceleration, Euler acceleration, and centrifugal acceleration terms.
In an Earth-fixed rotating reference frame, the horizontal displacement of a freely falling body receives contributions from Coriolis acceleration and centrifugal acceleration. A short-fall approximation substitutes the unperturbed downward velocity into the Coriolis term and the Earth's surface position into the centrifugal term. If gravitational acceleration excludes centrifugal acceleration, both contributions must be included explicitly.
For spherical mass density in the anelastic approximation for a rotating barotropic star, the displayed pressure amplitude gives velocity proportional to . This velocity is divergence free and tangent to spherical shells, so its mass-weighted divergence vanishes for every spherical mass density profile. It is an inertial r-mode driven by Coriolis acceleration; with phase its inertial frequency is .
In a connected inviscid uniformly rotating barotropic fluid, momentum balance makes the displayed sum constant. The pressure term is the barotropic enthalpy function. Perturbations experience Coriolis acceleration, and their rotating-frame frequency depends on the chosen exponential sign convention.
Besides the two propagating inertial-acoustic wave branches, a uniform barotropic Keplerian shearing sheet has a stationary branch balancing pressure against Coriolis acceleration. For radial wavenumber , setting in continuity gives , and radial momentum gives the displayed azimuthal balance. The full determinant is proportional to . At the stationary branch is a uniform column-density change; it is not a travelling density wave.