Russian LP record disk of ensemble "Asya kya" (1986)

An old record (or CD or DVD) demonstrates gyroscopic principles

Gyroscopic inertia – a strange, complicated word – is a force common all around us. It explains how we are able to ride a bike, how planes navigate, and how a figure skater is able to do those lightning-fast spins. Here’s a simple experiment that’ll clear up this confusing concept. Note: the hardest part of this experiment is going to be finding one of those old LP records.

Tie one end of the string to the middle of a matchstick or pencil.
Pull the other end of the string through the center of an LP record (so the matchstick is centered underneath the hole). You can also use an old CD or DVD.
Swing the record back and forth like a pendulum in smooth, even movements and note how effortlessly it glides back and forth.
Now give the record a spin.

What will happen when you try to swing the record again? What makes the record swing smoothly? Gyroscopic inertia is the property of a rotating object to resist any force which would change its axis of rotation. Once the record is set spinning at an angle perpendicular to the string, it will resist any forces (such as gravity) that try to change that angle.

Notes about the Rock and roll records that just won’t swing experiment

Gyroscope, also called a gyro, is a device that uses rotation to produce a stable direction in space. A basic gyroscope consists of a spinning wheel or ball, called the rotor, and a support system. Once the rotor is set in motion, the gyroscope resists any attempt to change its direction of rotation. Because of this property, gyroscopes are widely used in flight and navigation instruments. For example, a gyroscope is used to provide heading or course information that is unaffected by air turbulence or heavy seas.

Gyroscopic inertia is the tendency of a spinning body to resist any attempt to change the direction of its axis of rotation. For example, the earth spins around its axis, an imaginary line that connects the North and South poles. Because of gyroscopic inertia, the north axis of the earth continues to point to the North Star as the earth moves in its orbit around the sun.

Gyroscopic inertia enables the axis of a spinning gyroscope always to point in the same direction, no matter how the support of the gyroscope moves about. The magnitude (strength) of the inertia depends on the distribution of the weight of the rotor and the speed of its spin. Gyroscopes with most of their weight at the rotor’s rim have the greatest amount of inertia. Thus, a bicycle wheel makes a good gyroscope, but a pencil spinning on its point does not. In addition, the faster the rotor spins, the more gyroscopic inertia it possesses.

Precession is the tendency of a spinning body to move at right angles to the direction of any force that tries to change its direction of rotation. You can use precession to guide a rolling hoop. When you roll the hoop, it will not fall down if you push from the side against the top. In this case, the hoop merely turns a corner. The hoop precesses, or turns at right angles to the force that you have applied against it. Similarly, a spinning gyroscope will move at right angles to any force that attempts to change the direction of its axis. The earth itself precesses slightly. This turn occurs because the pull of gravity by the sun and moon tends to tip it over.