Negative frequency

In mathematics, the concept of signed frequency (negative and positive frequency) can indicate both the rate and sense of rotation; it can be as simple as a wheel rotating clockwise or counterclockwise. The rate is expressed in units such as revolutions (a.k.a. cycles) per second (hertz) or radian/second (where 1 cycle corresponds to 2π radians).

Example: Mathematically speaking, the vector ${\displaystyle (\cos(t),\sin(t))}$ has a positive frequency of +1 radian per unit of time and rotates counterclockwise around the unit circle, while the vector ${\displaystyle (\cos(-t),\sin(-t))}$ has a negative frequency of -1 radian per unit of time, which rotates clockwise instead.