Precession Torque

The spin angular momentumis along the rotation axis as shown, but the torque about the support point is in a direction perpendicular to the angular momentum. The torque produces a changein L which is perpendicular to L. Such a change causes a changein direction of L as shownbut not a change in its size. This circular motionis called precession.

If the wheel is not spinning, the apparatus just rotates downward toward a vertical orientation. If you curl the fingers of your right hand in the direction of that expected rotation, then your thumb will point perpendicular to the spin axis in the direction of the torque produced by gravity. The tip of the angular momentum vector, and therefore the axle of the wheel, will precess in that direction.

Index

Go to top view
 
HyperPhysics***** Mechanics ***** Rotation R Nave
Go Back





Precession, Top View

The spin angular momentumis along the rotation axis as shown, but the torque about the support point is in a direction perpendicular to the angular momentum. The torque produces a changein L which is perpendicular to L. Such a change causes a changein direction of L as shownbut not a change in its size. This circular motionis called precession.

Index

Go to side view
 
HyperPhysics***** Mechanics ***** Rotation R Nave
Go Back





Precession of Spinning Wheel

Load video

A spinning wheel which isheld up by one end of itsaxle will precess in thesense shown if it has that direction of spin. If the spin is reversed, it will precess in the opposite direction. The sense of precession is determined by the direction of the torque due to the weight of the spinning wheel. That torque is perpendicular to the angular momentum of the wheel.

Index

Vector rotation examples
 
HyperPhysics***** Mechanics ***** Rotation R Nave
Go Back