Another book that I've read recently, which matches the current sports season, is Football Physics: The Science of the Game, by University of Nebraska physics professor Timothy Gay.
Before reading the book, I thought that I would find it useful on at least two levels. First, most of the physics reading I've done during the past year and a half has been in the particle area; I thought that Football Physics would provide an accessible discussion of classical/Newtonian physics, that is, the study of large, everyday objects. Second, although I have always been a huge sports fan, I have been concerned for many years about the high injury rate in football. The book, I thought, would give me additional information on the physics of collisions and why players are so vulnerable. In both areas, I'm pleased to say, I got out of the book what I thought I would.
The book can be grouped into a number of different topics. Covered first is what might be called the physics of play in "the trenches." Blocking, tackling, collisions, quarterback sneaks, and offensive linemen exploding off the snap are all covered in the first two chapters. These chapters invoke physics concepts including Newton's laws of motion (such as the second law, where force equals mass times acceleration), momentum, torque, work, kinetic energy, and power. We learn that, for a linebacker such as Dick Butkus to stop a running back of a certain mass running at a certain speed, might take 1,150 pounds of force!
Next is the study of play in the open field: receivers' running of pass patterns (and timing with the quarterback), runners' "juking" to try to fake out defensive players, and defenders' pursuit of ball carriers (what fans might think of as who has the "angle"). Here we get vectors, Cartesian coordinates, and the Pythagorean theorem.
The projectile motion of the flying football (punted, kicked, and passed) takes up the next three chapters. Altitude, air drag, spiraling and spinning of the ball are all covered here, plus the mechanics of the kicking motion.
The study of players' football gear comes next, which is probably most relevant to my interest in football injuries. What I found most interesting is how the helmet serves a protective role. The surface or plastic shell of the helmet distributes the force of an incoming head-to-head hit more widely than if the recipient of the hit were not wearing a helmet (it hurts just thinking about the latter option!). Further, the padding within a helmet lengthens the duration of a collision, lessening the average force.
Another injury-related concern involves the type of turf in a stadium, either artificial turf (such as Astroturf) or natural grass. Old-fashioned artificial turf (carpet placed over a parking lot, with some thin padding in between) has been thought to create an injury hazard, due to its hardness and lack of "give" when a player plants his foot. Gay states that:
During the 1980s and mid-1990s, after a series of extensive studies, a consensus developed that playing football on Astroturf and its variants was, in fact, more likely to cause serious injury than playing on natural grass (p. 226).
(As Gay also notes, some newer hybrid surfaces have been introduced in recent years that appear to be more forgiving than old-fashioned artificial turf and perhaps safer; such hybrids include Field Turf and Sport Grass.)
In terms of the physics of turf, one important concept is friction. This area gets a little complicated, but a key distinction is between static friction (related to the traction or "grab" of the turf) and breakaway/sliding friction. Using the analogy of trying to pull apart connected pieces of Velcro, Gay notes that, "...the force required to initiate the sliding can be quite large, because each piece has its hooks firmly anchored in the other's 'loops.' Once the hooks have broken away, the sliding force becomes relatively small" (p. 233).
The final chapter, "Waves in the Stadium," concerns sound waves (noise) and fans doing the wave.
As Gay notes in the book, another contribution of his to popularizing physics within the football context is his appearance in short videos shown on the scoreboard at Nebraska football games, describing the physics of various football phenomena. Those video clips are also available on Gay's faculty website (click here).
Professor Gay also refers readers to a football physics site at the University of Tennessee.
In fact, nice tutorials have been written by a variety of authors on the physics of numerous different sports. In the months ahead, I will feature these tutorials.