A gyroscope is a rapisly-spinning symmetrical top usually used to maintain direction or to demonstrate the principles of angular momentum. Practical gyroscopes usually consist of a disc or spoked wheel transfixed by an axial rod about which it rotates, along with a cage-like structure to both support and protect the components. Gyroscopes used for demonstrations often have no motors, relying upon low-friction mounting to allow them to keep spinning for a long time. Gyroscopes used for measurement purposes will generally have some motor to provide constant uniform rotation.
