Popular Mechanics Why a Curveball Curves by Frank Vizard

Author:Frank Vizard
Language: eng
Format: epub
Publisher: Hearst

ROTATIONAL MOMENTUM

Not every shot requires a runaway train to propel it. Linear momentum can be generated in a single powerful step, much like a baseball player stepping into his swing prior to launching a moonshot over the centerfield bleachers. The friction generated as the shooter drives his foot into the turf is where linear momentum begins its conversion to rotational momentum, as the shooter transfers energy from his planted foot through his legs and hips, up the torso and into his shoulders—which will become the axis of rotation from which even greater speed can be applied to the ball before it is fired.

As the stick head with the ball pocketed inside rotates around the player’s body it picks up the speed it needs to become an effective shot. The linear speed of an object is directly proportional to its distance from the axis of rotation; the further away it is from the center, the greater the speed at which it moves. Think of two horses on a merry-go-round, both set even to each other as they travel around the carousel. If you drew the path of each horse you’d have a larger circle for the outside horse, and from that you’d conclude that in creating the larger circle the outer horse had to travel a greater distance, and to go further than its companion while maintaining an equal position it must have also travelled at a greater speed.

When the object in question is a lacrosse ball poised to scream through the air as if it were fired from a cannon, both arm movement and stick length determine the distance it travels around the shooter’s body. As Paul Rabil comes bearing down on a goalie, he can extend the head of his 40-inch lacrosse stick an additional 22 inches away from him in the course of a well-executed shot. With the ball in motion over five feet away from his shoulders, Rabil’s rotational momentum at the point of release has been measured at 1,350 degrees per second.

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