**Physics**

The speed of rotation is given by the angular frequency (rad/s) or frequency (turns/s, turns/min), or period (seconds, days, etc.). The time-rate of change of angular frequency is angular acceleration (rad/s²), This change is caused by torque. The ratio of the two (how heavy is it to start, stop, or otherwise change rotation) is given by the moment of inertia.

The angular velocity *vector* also describes the direction of the axis of rotation. Similarly the torque is a vector.

According to the right-hand rule, the direction away from the observer is associated with clockwise rotation and the direction towards the observer with counterclockwise rotation, like a screw.

See also: Speed#Tangential Speed, rotational energy, angular velocity, Centrifugal force (fictitious), centripetal force, circular motion, circular orbit, Coriolis effect, spin (physics), rotational spectroscopy, and Rigid body dynamics#Rigid body angular momentumRead more about this topic: Rotation

### Famous quotes containing the word physics:

“We must be physicists in order ... to be creative since so far codes of values and ideals have been constructed in ignorance of *physics* or even in contradiction to *physics*.”

—Friedrich Nietzsche (1844–1900)

“The pace of science forces the pace of technique. Theoretical *physics* forces atomic energy on us; the successful production of the fission bomb forces upon us the manufacture of the hydrogen bomb. We do not choose our problems, we do not choose our products; we are pushed, we are forced—by what? By a system which has no purpose and goal transcending it, and which makes man its appendix.”

—Erich Fromm (1900–1980)