11.13 : Gyroscope

A gyroscope is defined as a spinning disk in which the axis of rotation is free to assume any orientation. When spinning, the orientation of the spin axis is unaffected by the orientation of the body that encloses it. The body or vehicle enclosing the gyroscope can be moved from place to place, while the orientation of the spin axis remains the same. This makes gyroscopes very useful in navigation, especially where magnetic compasses cannot be used, such as in crewed and crewless spacecraft, intercontinental ballistic missiles, crewless aerial vehicles, and satellites like the Hubble Space Telescope. Gyroscopes used in guidance systems to indicate directions in space must have an angular momentum that does not change in direction. When placed in the vehicle, they are put in a compartment that is separate from the main fuselage. Changes in the orientation of the fuselage do not affect the orientation of the gyroscope. In airplanes, a heading indicator attached to a gyroscope provides navigation. When the airplane's direction changes, an angular change in the heading indicator occurs.

Gyroscopes possess two properties—rigidity and precession. Rigidity is the property of a spinning gyroscope to retain its direction of spin. Precession is the change in orientation of the gyroscope due to a force applied perpendicular to its rotational plane. The precession of a gyroscope can be demonstrated by a spinning top. If the top is placed on a flat surface near the surface of the Earth at a vertical angle and is not spinning, it will fall over, due to the force of gravity producing a torque acting on its center of mass. However, if the top is spinning on its axis, it precesses about the vertical direction, rather than topple over due to this torque. This is due to the torque on the center of mass, which provides the change in angular momentum.

This text is adapted from Openstax, University Physics Volume 1, Section 11.4: Precession of a Gyroscope.