Gyroscope

Gyroscope, heavy spinning disk mounted so that its axis is free to adopt any orientation. The fact that a spinning top will stay upright as long as it is spinning fast enough demonstrates the property of gyroscopic inertia: the direction of the spin 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.