Gyroscope
A spinning disk on a tilted axis. Gravity pulls it down, but angular momentum redirects the fall into steady precession. Toggle gravity off and the magic stops.
Ωprecession = mgr / (Iω)
About this lab
A gyroscope is a spinning body whose axis of rotation resists changes in orientation. When tilted and released, gravity exerts a torque perpendicular to the spin axis. Instead of falling over, the gyroscope precesses — its axis traces a slow circle around the vertical. The precession rate is Ω = mgr / (Iω), where m is the rotor mass, g is gravitational acceleration, r is the distance from the pivot to the center of mass, I is the moment of inertia, and ω is the spin angular velocity.
Conservation of angular momentum is the key principle. The torque from gravity changes the direction of the angular momentum vector without changing its magnitude, producing steady precession. At very high spin rates the precession slows; at low spin rates the rotor may also nutate — a rapid wobble superimposed on the slower precession.
Gyroscopic effects appear everywhere in engineering and nature. Navigation gyroscopes maintain reference frames in aircraft and submarines. A bicycle stays upright partly through gyroscopic precession of the wheels. Spacecraft use reaction wheels (essentially gyroscopes) to change orientation without expelling propellant. The Hubble Space Telescope used six gyroscopes for pointing stability, and the principle dates back to Foucault (1852), who coined the name from Greek: gyros (circle) and skopein (to see).