Newton's Laws for Rotation

It is simplest to view the torque as consisting of two pieces:

• One part that has the same direction as the object's rotation axis, and
• One part that is at a right angle to the rotation axis.

The portion of the torque that lines up with the object's rotation axis will change its angular speed, just the way that a linear force acting along the direction that an object is sliding will change its linear speed - it will speed up if they act in the same direction, or slow down if they are in opposite directions.

The part of the torque that acts at a right angle to the spin direction will not make the object's rotation speed up or slow down, however. It will change the spin direction - a phenomenon known as precession.

Precession Torque (Standard View)

Precession Torque (Top View)

Return to rotational statements of Newton's laws.