# Double Bicycle Wheel

#### Abstract

A double bicycle wheel demonstrates addition and cancellation of angular momentum vectors: when the wheels spin in opposite directions there is no net angular momentum and the wheels can be tipped easily.

Yes

#### Principles Illustrated

Two bicycle wheels on a common axle will have a net angular momentum when the wheels spin in the same direction but will have zero net angular momentum spinning at the same speed in opposite directions. Angular momentum as a vector. With the wheels spinning in the same direction the angular momentum vectors of the wheels are both along the axle in the same direction and add. When the wheels spin in the opposite direction the angular momentum vectors cancel and the wheel tips easily. There is no gyroscope effect.

#### Instructions

Have a student support the wheel set by holding the axel on both sides. Have a strong student spin the wheels as fast as possible in the same direction. The gyroscope effect is obvious. Now repeat with the wheels spinning in the opposite direction. There is no noticeable gyroscope effect if the wheels are spun at least close to the same speed. The wheel will topple if one attempts to dangle it by a string attached to the end of the axle as is done with a single bicycle wheel.

#### Safety

Keep fingers out of the spokes! Also the weighted wheels make the apparatus fairly heavy.

Individual teachers are responsible for safety in their own classes. Even familiar demonstrations should be practised and safety-checked by individual teachers before they are used in a classroom.