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Letter: Physics and the effect of headers

New York Cosmos forward Gaston Cellerino makes a

New York Cosmos forward Gaston Cellerino makes a header during the first half of the NASL Soccer Bowl against the Ottawa Fury at Shuart Stadium on Sunday, Nov. 15, 2015. Credit: James Escher

I would like to disagree with a statement attributed to Dr. Kevin Crutchfield, a neurologist who works with athletes [“Soccer’s hard knocks,” News, Dec. 18].

Crutchfield was quoted as saying that a properly executed “header” — when a soccer player uses her head to hit a ball — is not considered a serious risk for concussion because “you can put more force on the ball than the ball puts on you, and then there’s no energy transfer into the brain.”

This quote contradicts Newton’s third law of motion: For every action there is an equal and opposite reaction. In accordance with Newton’s law, the correct statement would be, you can put the same force on the ball that the ball puts on you.

Although the size of the force acting on the player and ball are the same, the effect of the force is what’s different. Because the player has a much larger mass than the ball, Newton’s second law tells us that the acceleration experienced by the player is much smaller than the acceleration experienced by the ball. The much smaller acceleration of the player (and hence the player’s brain) is what minimizes the energy transfer into the brain.

Mark Hogan, Ronkonkoma

Editor’s note: The writer is a college physics professor.



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