Precession

Definition

Precession is the gradual change in the orientation of the rotational axis of a rotating body. It occurs due to an external torque acting on the body.

5 Must Know Facts For Your Next Test

1. Precession occurs when a gyroscope or spinning object experiences a torque perpendicular to its angular momentum.
2. The rate of precession is directly proportional to the applied torque and inversely proportional to the angular momentum of the gyroscope.
3. In mathematical terms, precession can be described by $\Omega = \frac{\tau}{L}$ where $\Omega$ is the precessional angular velocity, $\tau$ is the torque, and $L$ is the angular momentum.
4. Gyroscopes are commonly used in navigation systems because their precessional properties help maintain orientation.
5. Earth’s axis undergoes precession with a period of approximately 26,000 years due to gravitational forces exerted by the Sun and Moon.

Review Questions

• What causes precession in a gyroscope?
• How does increasing angular momentum affect the rate of precession?
• Write down and explain the formula for precessional angular velocity.

Related terms

Angular Momentum:

A vector quantity representing the rotational inertia and rotational velocity of an object. Denoted as $L = I \omega$ where $I$ is moment of inertia and $\omega$ is angular velocity.

Torque:

A force that causes an object to rotate around an axis. It is given by $\tau = r \times F$, where $r$ is position vector and $F$ is force.

Gyroscope:

A device consisting of a wheel or disk mounted so that it can spin rapidly about an axis which is itself free to alter in direction.