Momentum and Energy


How can athletes use angular momentum?

Let’s explore two different sports. In platform diving a person pushes off the tower, and thus the platform exerts a force on her (Newton’s Third Law). But, if she isn’t standing straight up, the force also exerts a torque on her, and starts her rotating. If she pulls her arms and legs in, then her mass is closer to her axis of rotation, and her speed of rotation increases. To slow this rotation, she can extend her arms and legs. With good timing, she can hit the water with a bare minimum of rotation.

Consider a figure skater. She can start spinning on the point of one skate by pushing on the ice with the second skate. Again, the force of the ice exerts a torque, and so her rotational speed increases. She can extend her arms to slow the rotation, or pull them in as close as possible to attain the highest spin rate.


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