Although the scientific gyroscope was only devised by Jean Foucault in the mid-19th century, the child's traditional spinning top demonstrates the gyroscopic principle. The fact that it will stay upright as long as it is spinning fast enough demonstrates the property of gyroscopic inertia: the direction axis resists change. This means that a gyroscope mounted universally, in double gimbals, will maintain the same orientation in space however its support is turned, a property applied in many navigational devices.
A gyroscope of moment of inertia I and spinning with angular velocity S about a horizontal axis with one end mounted on a vertical mounting will precess (see precession in a horizontal circle about the mounting with angular velocity ω = T/S where T is the torque acting on the gyroscope about the mounting due to its weight.
Instrument gyroscopes usually consist of a wheel having most of its mass concentrated at its rim to ensure a large moment of inertia and which is kept spinning in frictionless bearings by an electric motor. Once the wheel is set spinning its response to applied torques can be monitored or used in control servomechanisms.
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