Gyroscope

Introduction

A symmetrical object rotating about an axis, one point of which is fixed, is called a top. If the fixed point is at the center of gravity, the top is called a gyroscope. A spinning top has an angular momentum because it is spinning around its long body axis and because it has a mass distributed around that axis. The angular momentum is changed by a torque which is a result of gravity attracting the top through its center of mass. As a result, the top tends to rotate about a vertical line from its point of contact with the surface in a motion called precession, thus moving in a motion that maps out a cone. In a gyroscope, the spinning top is confined to a ring or set of rings that permit it to turn freely in any direction. The axis of a free gyroscope will remain fixed with respect to space, provided no external forces act upon it. By applying the appropriate torque, a gyroscope can be made to turn in any direction. The gyroscope, as shown in Figure 1, does not fall because the upward force at the pivot is just equal to its weight. Thus, the resultant vertical force is zero and the vertical acceleration is zero. Instead, the gyroscope precesses in a horizontal direction, rotating around the fixed point. The ability of a gyroscope to maintain its orientation makes it useful as a direction indicator.

Concepts

• Angular momentum
• Torque
• Forces
• Rotation of the Earth
• Center of gravity
• Symmetry

Safety Precautions

Do not use the gyroscope on surfaces that are easily scratched or near breakables. Use the gyroscope only in the manner for which it is intended.

References

Special thanks to David A. Katz, retired, Wilmington, DE, who provided Flinn Scientific with the instructions for this activity.