Introduce the unit vectors ı ı ^ ^ , ȷ ȷ ^ ^ , k ^ ^ representing standard unit basis vectors in the rotating frame. The time-derivatives of these unit vectors are found next. Suppose the frames are aligned at t = 0 and the z -axis is the axis of rotation. Then for a counterclockwise rotation through angle Ω Ω t : ı ı ^ ^ ( t ) = ( cos ⁡ ⁡ θ θ ( t ) , sin ⁡ ⁡ θ θ ( t ) ) where the ( x , y ) components are expressed in the stationary frame. Likewise, ȷ ȷ ^ ^ ( t ) = ( − − sin ⁡ ⁡ θ θ ( t ) , cos ⁡ ⁡ θ θ ( t ) ) .