Definition:Precession

Definition

Let $B$ be a body rotating in space about an axis $A$.

Let $B$ be subject to an external torque $\mathrm T$.

Precession is the change in the direction of $A$ which is perpendicular to the direction of $\mathrm T$.

Examples

Spinning Top

Consider the child's toy the spinning top $T$.

When $T$ is set in motion, it is often the case that the axis of $T$ is not vertical.

If that is the case, then the tip of the axis describes a circular path, which gives the motion of $T$ a "wobble".

This is caused by precession.

Earth's Axis

The precession of the axis of rotation of Earth makes a full revolution in about $25 \, 800$ years.

Also see

• Results about precession can be found here.

Sources

• 1998: David Nelson: The Penguin Dictionary of Mathematics (2nd ed.) ... (previous) ... (next): gyroscope
• 1998: David Nelson: The Penguin Dictionary of Mathematics (2nd ed.) ... (previous) ... (next): precession
• 2008: David Nelson: The Penguin Dictionary of Mathematics (4th ed.) ... (previous) ... (next): gyroscope
• 2008: David Nelson: The Penguin Dictionary of Mathematics (4th ed.) ... (previous) ... (next): precession