The time, space, and velocity scales are important in determining the importance of the Coriolis force. Whether rotation is important in a system can be determined by its Rossby number, which is the ratio of the velocity, U, of a system to the product of the Coriolis parameter, f = 2 ω ω sin ⁡ ⁡ φ φ , and the length scale, L, of the motion: