would a gyroscope spin indefinetly in space?
I know aircraft use them, but would they serve any purpose without gravity?
They certainly are useful in space, because they spin for a really long time (infinite, in theory, but long in practice). Because their angular momentum vector points in a constant direction, satellites and space stations can use gyroscopes to orient themselves.
Gyroscopes are essential for spacecraft. The axis of the spinning flywheel tends to stay pointed in the same direction, with or without gravity. You can use it anywhere as a reference to measure the orientation of your vehicle, be it an aircraft or spacecraft.
Since the flywheel is mounted on bearings, there is friction. So it won’t spin indefinitely. Even if you use magnetic bearings and high-grade vacuum, friction with the few remaining air molecules will slow it down measurably. In fact, this is sometimes used to measure the pressure at extremely low pressures, down to 10[sup]-7[/sup] torr or so. You use magnetic fields to levitate a tiny metal ball, set it spinning and meaure the rate at which it slows down.
Gravity has nothing to do with the purpose of a gyroscope.
A gyroscope is essentially a flywheel designed to have a constant angular momentum. Frictional losses are compensated for by powering the gyro to maintain the design RPM. The principle is simple - a body in a state of motion or rest will tend to remain in that state unless acted upon by an external force. By removing (or compensating for) the external forces, the angular momentum vector will always act in the same direction. Your car engine has a flywheel, but in a car, that flywheel is constrained so that it turns when your car turns. In a gyroscope, the flywheel is suspended by an arrangement which does not constrain its rotational degrees of freedom. The gyro housing (and whatever vehicle it may be attached to) can rotate in any direction, and the gyro will maintain its initial orientation.
As the vehicle (ship, aircraft, satellite, etc.) moves in space, the gyro flywheel maintains its direction within the gyro housing. Of course, you can never get rid of all of the frictional losses, so to maintain accuracy the gyro flywheel must have a large angular momentum in comparison to the friction in the bearings of the suspension. Encoders on the suspending apparatus detect the angular rotations to precisely determine the vehicle’s orientation. In addition to attitude, you can also use gyros to obtain accelerations - meaning that as long as you know a vehicle’s initial position, attitude and velocity, it is possible to use inertial navigation (using gyroscopes) to determine these values at a later time. Autonomous underwater vehicles (AUV’s) and some submarines make use of this, since the satellite signals provided by the GPS system do not propagate through water.
Fascinating topic, really. It’s enough to make your head spin…
“would a gyroscope spin indefinetly in space?”
What’s your definition of “indefinitely”? Planet earth has been spinning like a gyroscope in space since I was a little boy. History books tell me that it’s been a bit longer than that.