Siacci's Theorem

Siacci's theorem, a result in kinematics associated with the Italian mathematician Francesco Siacci, gives an alternative way to decompose the acceleration of a particle moving along a curved path into radial and tangential components, in contrast to the standard decomposition into mutually perpendicular normal and tangential components. Under Siacci's decomposition the radial and tangential components are generally not perpendicular to each other, but the approach proves especially useful for motions in which angular momentum is conserved.