08 Precession (3a)

Aim¶

To show how a rotating wheel reacts to an applied torque.

Subjects¶

• 1Q50 (Gyros)

Diagram¶

Equipment¶

• bicycle wheel with handles

• 1 piece of rope

• 1 stick

Presentation¶

The wheel is rotating and held by a string. The rotating wheel has an angle of about $45^{\circ}-60^{\circ}$ with the vertical. The wheel will precess about a vertical axis. When the instructor pushes with the side of his hands or a stick against one of the handles of the wheel in the direction of precession, then the rotating wheel will rise to a more vertical position. This can be continued, even passing the vertical.

Explanation¶

The rotating wheel will precess due to gravitational torque, $m g s$ ( $I \omega_{0}$ moves in the direction of this gravitational torque; precession) (see Figure 2a).

$F$ is the applied force in the direction of precession (see Figure 2b). The applied torque is pointing vertically upward, so now $I \omega_{0}$ moves also upward.

Video Rhett Allain¶

Sources¶

• Freier, George D. and Anderson, Frances J., A demonstration handbook for physics, pag. M-53

• Sutton, Richard Manliffe, Demonstration experiments in Physics, pag. 79