Angular Momentum

To keep angular momentum from getting too complicated, we will think of the figure skater as a simple rigid body. Through figure skating, the concept of angular momentum can be best described  by what we see happen when a skater is spinning slowly with her arms and legs out wide and then as soon as she pulls her arms in, the speed of her spinning increases significantly. This is a good example of the law of conservation of momentum. From Randall Knight’s Physics for Scientists and Engineers textbook, the conservation of angular momentum is explained as follows: “The angular momentum L of an isolated system (net Torque = 0) is conserved. The final angular momentum Lf is equal to the initial angular momentum Li. Both the magnitude and direction of L are unchanged.” Another idea to note is the equation for angular momentum: L=Iω (angular momentum = moment of inertia x angular velocity). With these facts in mind, lets think about what is happening when a skater is spinning. When a skaters arms and legs are outstretched, her moment of inertia has a large magnitude and her angular velocity has a small magnitude. If she starts pulling in her arms, we can visibly see that her angular velocity has increased and thus we can deduce that in order to satisfy the law of conservation of angular momentum her moment of inertia has decreased.

angular momentum