Figure skaters spend a lot of time either spinning on the ice or rotating through the air. The faster a skater can spin, the more impressive that spin will be to the judges. Additionally, in the skater's short program, there is a minimal required number of revolutions a skater must complete in his or her spins. To spin fast, or for a long time, the skater must develop a large amount of angular momentum. The speed of rotation during a skater's jump is also affected by his or her angular momentum. The ability of the skater to rotate faster in the air depends greatly on the skaters angular momentum.
 Several spins and jumps have been chosen to illustrate the generation and conservation of angular momentum. Before proceeding to this analysis section, you need to be familiar with some basic physics principles and definitions. For example, it is important to understand the concepts of force, angular displacement, angular velocity, and momentum to fully comprehend the analysis of the figure skating jumps and spins. If you need refreshing on the definitions of these terms, proceed to the glossary before continuing this unit.

## Objectives

The objectives of this unit is to use example from figure skating to become familiar with the concept of conservation of angular momentum, to be able to solve basic angular momentum problems, and to learn great examples from figure skating for teaching the conservation of angular momentum to your students.

## Definition

Conservation of angular momentum is the principle that the angular momentum of an object remains constant as long as no external torque, or moment, acts on that object. When a figure skater is in the air, he or she is rotating about his or her center of mass and possess a certain amount of angular momentum. The only external force is gravity. However, gravity acts vertically down through the center of mass (COM) of the skater. Since gravity acts through the axis of rotation of the skater, it does not cause a torque and can not change the skater's angular momentum.

© April, 1998, Montana State University-Bozeman