Spinning TARDIS Ring

Why Does the TARDIS Spin?

Conservation of angular momentum. Within the reference frame of being parked, the TARDIS is never spinning. Therefore, while in the Vortex, the TARDIS has to spin up or spin down to jump from the angular momentum of the previous planet to the angular momentum of the surface of the target. On planets, our reference frame is fixed to the planet. In the Vortex, rather than using the slightly non-inertial planetary surface as the frame, we use a truly inertial reference frame behind the TARDIS. Quoted from Silvarus

Makes perfect sense to me!

Ring size 7.