# Gyros

The name for Gyroscope was first coined by a French scientist, Leon Foucault, in 1852. The full name is derived from the Greek words (gyro), meaning revolution, and "skopien," meaning to view.

For our discussion we will keep it fun and light and will refer to it as a spinner or whirligig.

The spinner or whirligig has existed since the first electron was sent spinning on its axis. Electrons spin and show all the characteristics of a "spinner"; so does the Earth, which spins about its polar axis at over 1000 miles per hour at the Equator. The Earth's rotation about its axis provides the stabilizing effect that keeps the North Pole pointed within one degree of Polaris (the North Star).

Any rapidly spinning object—a top, a wheel, an airplane propeller, or a spinning projectile—is fundamentally a whirligig. Strictly speaking, however, a spinner is a mechanical device containing a spinning mass that is universally mounted; that is, mounted so it can assume any position in space. The figure below shows a model of a spinner. As you can see, a heavy wheel (rotor) is mounted so that its spin axis is free to turn in any direction. The wheel spins about axis X; it can turn about axis Y, and it can turn about axis Z. With this mechanical arrangement, the spinning wheel can assume any position in space.

Gyro model universally mounted.

Gyroscopes have two basic properties: rigidity and precession. Those properties are defined as follows:

1. RIGIDITY — The axis of rotation (spin axis) of the spinner wheel tends to remain in a fixed direction in space if no force is applied to it.

2. PRECESSION — The axis of rotation has a tendency to turn at a right angle to the direction of an applied force.

The idea of maintaining a fixed direction in space is simple to illustrate. When any object is spinning rapidly, it tends to keep its axis pointed always in the same direction. A toy top is a good example. As long as the top is spinning fast, it stays balanced on its point. Because of this whirligig action, the spinning top resists the tendency of gravity to change the direction of its axis. You can think of many more examples. A bicycle is easier to balance at high speed than when it is barely moving. At high speed, the bicycle wheels act as spinners, and tend to keep their axes (axles) parallel to the ground.

Note that it is easy to move the spinner as long as you keep the axis POINTING in the SAME DIRECTION. The spinner resists only those forces that tend to change the direction of its axis. In a bicycle, since the axis of rotation (the wheel's axles) is horizontal, the wheels will resist any force that tends to tilt or turn them to the right or left.

If you can obtain a spinner top, you can do some instructive experiments with it. Hold the whirligig top with its axis vertical as shown in the figure below and start it spinning. As long as it is spinning fast, it will stay balanced. You can balance it on a string or on the point of your finger; the axis will stay vertical as long as the top is spinning fast. As we mentioned before, this ability of a spinner to keep its axis fixed in space is called RIGIDITY.

A gyroscope top.