When Ray Lewis chases Tiki Barber and drags him down onto the turf, it may not look pretty, but he's actually employing some elegant, precise laws of physics, including: p = m*v.
In other words, the Baltimore Raven linebacker's momentum equals his mass times his velocity and when applied, exceeds that of the New York Giant's running back. Or, put another way, a big, fast-moving player like Lewis can hit hard — really hard.
Contact, lots of it, is why several university physicists like to use football as a model for energy in motion and the transfer of energy. One physicist, Tim Gay, of the University of Nebraska, even offers football fans quick lessons in the science during halftime at his university's home games.
Lately, physicists like Gay have noticed the figures for such equations are bigger and bigger, leading to harder and harder tackles. But just as physics dictates what makes a hard, bone-crunching tackle, physicists say it can also play a role in reducing injuries.
Bigger Players, Bigger Damage
Consider, for example, the "Refrigerator." William Perry, the 300-pound defensive lineman was viewed as a behemoth during his days playing for the Chicago Bears in the mid- 1980s to early '90s. Now most professional teams feature entire defensive and offensive line-ups of appliance-sized players.
Thanks to advances in nutrition and training, players have also become faster. Recent studies show repeated collisions by big, fast-moving bodies gradually, if not immediately break the body down.
One Los Angeles Times survey found that 78 percent of retired NFL players reported some kind of physical disability. Another study determined professional football players' life spans are 11 years shorter than the average man.
So how can players use physics to preserve their bones from the ever harder crunch of on field tackles? According to Gay, coaches have already provided most of the answers.
"I've found that even though most coaches have never taken a physics course, what they tell their guys is right on," says Gay.
Physics of Protection
For example, a common football tip to stay low and keep the head up while tackling, is actually just good physics, according to Gay.
"By keeping the feet planted and the head up, a player can direct where the force of an impact goes," he says. "By directing the force you can make sure either your equipment or the ground absorbs the shock."
Controlling the force of a tackle is just as important for a 300-pound lineman as it is for a 220-pound quarterback who's taking the hit. That's because when players collide, the force of the impact is distributed equally between them, thanks to a seemingly counter-intuitive law discovered by Sir. Isaac Newton in the 17th century.
Newton's third law of motion says if two objects interact, they exert opposite and equal forces on each other.
"Let's say a bigger player has a momentum of +10 and a smaller player is standing still and has a momentum of 0," Gay explains. "After they hit each other the bigger player's momentum is +5 and the little player's momentum is +5. But the bigger player will most likely determine where they end up."
Even if a player can't control a hit, says David Haas, a physics professor and football buff at North Carolina State University, good players learn to absorb impact in the right places.