Precession is a change in the
orientation of the rotational axis of a
rotating body. In an appropriate
reference frame it can be defined as a change in the first
Euler angle, whereas the third Euler angle defines the
rotation itself. In other words, if the axis of rotation of a body is itself rotating about a second axis, that body is said to be precessing about the second axis. A motion in which the second Euler angle changes is called
nutation. In
physics, there are two types of precession:
torque-free and torque-induced.