Article
Article
Precession
Article By:
Barger, Vernon D. Department of Physics, University of Wisconsin-Madison, Madison, Wisconsin.
Last reviewed:January 2020
DOI:https://doi.org/10.1036/1097-8542.542200
The motion of an axis fixed in a body around a direction fixed in space. If the angle between the two is constant so that the axis sweeps out a circular cone, the motion is pure precession; oscillation of the angle is called nutation. An example of precession is the motion of the Earth's polar axis around the normal to the plane of the ecliptic; this is the precession of the equinoxes. A fast-spinning top, with nonvertical axis, which precesses slowly around the vertical direction, is another example. In both examples the precession is due to torque acting on the body. Another kind of precession, called free or fast precession, with a rate which is comparable to the rotation rate of the body, is seen, for instance, in a coin spun into the air. See also: Nutation (astronomy and mechanics); Precession of equinoxes
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