I was studying about the derivation of coriolis force and centrifugal force for a particle i.e. the relation between the accelerations of a particle with respect to inertial and uniformly rotating frame of reference in which the z axis and the origin of both frames co incide with each other and after some time i stuck to the following expression-
$$ \bigg(\frac{d^2r}{dt^2}\bigg)_{S_0}=\bigg(\frac{d}{dt}\bigg)_{S}\bigg[\bigg(\frac{dr}{dt}\bigg)_{S}+\omega×r\bigg]+\omega\bigg[\bigg(\frac{dr}{dt}\bigg)_{S}+\omega×r\bigg].$$
In this expression, $$\bigg(\frac{dr}{dt}\bigg)_{S}+\omega×r$$ is the velocity of the particle with respect to Inertial frame so how can we differentiate this quantity with respect to another frame S (which is a rotating frame). I am unable to imagine and visualise this entire equation.
Can anybody help me for its deeper understanding?