# Lessons from HuskerVision

Punting: To punt the farthest, you must connect with what kickers call the 'sweet spot' on the football. Physicists like University of Nebraska physics Prof. Tim Gay call it the 'center of percussion.' This is the spot on the ball where the transfer of energy from the punter's foot to the ball is the most efficient. It's an oblong spot about 5 cm (2 in.) long, Gay estimates.

The moment when a kicker connects with the ball, the speed at which it leaves his foot, even the altitude of the playing field, all of these affect a ball's flight.

If a punter's knee is partially bent when his foot hits the ball, the energy transfer from kicker to ball is incomplete. But if the ball meets the player's foot at the instant his knee is locked and his leg fully extended, maximum energy transfer occurs and the ball soars downfield.

Altitude can be a big factor. 'You can get about 5 or 6 yards more ... in Boulder, Colo., than in Lincoln, Neb.,' Gay says, 'just because of the lower air pressure.' The 'thinner' air at high-altitude Boulder means there's less drag, or air friction, on the ball.

Tackling: Sir Isaac Newton could have told you a thing or two about tackling, though football was two centuries in the future when he was around. Sir Isaac's Third Law of Motion states that for every action or force, there is an equal and opposite reaction. Great tacklers, like Nebraska's Keyuo Carver [see photo, next page], apply this law. The harder Keyuo pushes into the ground, the more force it exerts on him, and thereby to his opponent.

'He extends through his legs,' Gay observes, 'so the ground is exerting a huge force. His head is up, and he's extending his body -and just cleans those people.'

But when two players collide in midair (as in an over-the-top goal-line plunge), different rules apply. 'You have pure conservation of momentum,' Gay says. This is a consequence of Newton's Second and Third Laws.

Conservation of momentum states that total momentum in an isolated area cannot change. In other words, if opposing players of the same mass (weight) collide at the same speed, they will fall straight down. But if the players have unequal momentum (mass times speed), the player with greater momentum will control the direction of the collision - whether into the end zone or away from it.

Passing: Does a football thrown in a tight spiral travel farther than one that's not spinning as fast? No, not necessarily.

The football's rate of spin 'is essentially irrelevant to how far it goes,' Gay says. The spin does reduce the drag (air friction) on the ball. It also stabilizes the ball in flight. This is the principle of angular momentum. It's the same principle that keeps a gyroscope stable.

If a quarterback wanted to put maximum spin on the ball, he would hold the ball right in the middle. No quarterback does this, however. They get the most directional control and power by holding the football toward the back. That way, they can push the ball forward with their hands.

There's still a physics mystery involved in throwing a football. Sometimes, the tip of a thrown football will angle up and then angle down as it flies. Other times, the point of the ball stays in the same angle throughout its flight. A ball that points up and then angles down meets less air resistance, so it travels farther. It's also easier to catch. But physicists can't tell quarterbacks how to do that every time - yet.

(c) Copyright 2000. The Christian Science Publishing Society

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