The rotating frame of reference introduces some interesting pseudo-forces into the equations through the material derivative term. Consider a stationary inertial frame of reference K , and a non-inertial frame of reference K ′ , which is translating with velocity U ( t ) and rotating with angular velocity Ω Ω ( t ) with respect to the stationary frame. The Navier–Stokes equation observed from the non-inertial frame then becomes