The science of Super Bowl

When Super Bowl 56 (or LVI, as the Americans prefer) kicks off today between two surprise teams with a combined 12 losses, most viewers will be talking about the unpredictability of sports and focussing on a game that has stood the test of time as a magnificent combination of athleticism and the move, countermove, counter-countermove type of thinking more commonly associated with chess.

But football also involves a startling amount of science.

One football scientist is Timothy Gay, an experimental physicist at the University of Nebraska, Lincoln, who in 2005 literally wrote the book: The Physics of Football.

One thing Gay did was to calculate some of the forces involved in the game. Not surprisingly, they are enormous. According to Gay, when a 100-kilogram linebacker and a 100kg running back collide shoulder-to-shoulder at about 10 metres per second (roughly the speed of Usain Bolt at his best), they hit with a force of about 3/4 of a US ton (75,000 kg). If it’s helmet-to-helmet, it’s more like 3/5 of a ton, because the impact happens more quickly.

And collisions aren’t the only things in football that involve forces several times the weight of a loaded refrigerator.

“When a kickoff return artist does a sharp juke to the left or right,” Gay says, “that’s about 800 pounds [360kg] through the ankle.”

Future sight

The timing required for a quarterback to launch a football accurately enough to place it perfectly in the hands of a wide receiver streaking toward the end zone can seem supernatural. To do this, Gay found, the quarterback has to throw the ball several seconds in advance of the intended catch, aim for the spot where his receiver is expected to be, and fire off the pass with exactly the right speed and upward angle to hit the receiver at just the right time. There’s a little bit of slack due to the ability of the receiver to look back and adjust course, but it’s not much. “You have to get the timing down to a tenth of a second,” Gay says.

Richard Price, a former high school and college football player who is now a senior lecturer at Massachusetts Institute of Technology, is impressed by the brainpower it takes to do this. “I’m a physicist and applied mathematician,” he says. “I greatly respect intelligence. But I cannot figure out how quarterbacks do what they do with their brains. They are watching in a small number of seconds the development of a complex chessboard in which they have to keep track of everything going on – and there is a lot going on. How are they doing that in [such] a limited amount of time?”

He compares championship gridiron to the difference between ordinary chess and speed chess (in which players are given very limited time in which to make their moves). The former gives you lots of time to think. The latter is played on something akin to reflex and pattern recognition. Intriguingly, the day after I talked to Price about this, the Wall Street Journal published an article saying that Cincinnati Bengals quarterback Joe Burrow is very good at a super-fast version of speed chess, in which each player has just two minutes to complete their entire side of the game.

Perhaps someday, Price suggests, neuroscientists might look at the type of brain function involved in this type of rapid-fire decision-making and analysis and compare the brains of those who are good at it to those who (like physicists and mathematicians) attack problems more methodically). But as far as he knows, no such research has ever been attempted.

Dark force

A part of football science that has been studied extensively is how best to protect football players’ brains from those 3/5  ton collisions.

One person working on this is William Moss, a physicist at Lawrence Livermore National Laboratory, in California. Working with colleagues at Boston University, he has concussed mice, designed computer models, experimented with synthetic heads filled with brain analogues he compares to tofu, and come to some important conclusions.

One major discovery has been that not all types of head impacts are the same. If you hit mice with what he calls a “focal deposition of energy” – roughly the equivalent of banging them on the head with a rock – they all become concussed. But when his team hit them with an equally powerful shock wave, he says, “none were concussed”.

The reason, they found in their computer models and tofu-brain experiments, was that focussed deposition of energy causes “a bloom of shear stress that goes into the brain”.

“It’s the shear stress that causes the concussion,” he says.

This doesn’t mean that shockwave-style impacts are harmless – repeated too often, they are believed to cause a type of cumulative brain damage known as chronic traumatic encephalopathy (CTE). But the discovery means that designing helmets to distribute impact forces and prevent concussions isn’t necessarily enough to protect against CTE. Rather, they also need to reduce the force being felt by the head as a whole.

The answer to that is padding.  “That’s basically how helmets work,” Moss says.

This season, some teams practiced with additional layers of padding placed on top of their normal helmets.

Spiralling to victory

Another element of football science involves the flight of the ball in the air. A lot is involved, but the most interesting questions have long circled around the spiral pass.

In the perfect spiral, the ball’s nose is always pointed in the direction in which it’s travelling: out of the quarterback’s hand, across the top of its arc, and down into the receiver’s arms.

It seems so natural that most people take it for granted, but for physicists it’s long been a conundrum.

That’s because the ball is spinning. This makes it a gyroscope, and a gyroscope should retain the same axis of rotation all the way up and over its arc, coming all the way back down with its nose still pointed in the direction it was pointing at the moment of release.

Spacecraft use gyroscopes for stabilisation. But they don’t, on their own, change angle the way a spiral pass does in flight.

Physicists had wondered about this for years – until 18 months ago, in a paper in the American Journal of Physics, Price, Moss, and Gay finally figured it out.

It turns out to be based on an exotic application of a principle all physics students know.

A gyroscope is like a top, and if you’ve ever played with a top you know that if you spin it tilted a bit off vertical on a stable surface, its axis will move in a slow circle. It’s a process called precession (some people call it a wobble), and it comes from how the spinning top resists the force of gravity trying to topple it over.

A spiral pass isn’t sitting on a table and isn’t being torqued sideways by gravity. But as it progresses through its arc, the air resistance goes from straight onto its nose to sideways. Price, Moss, and Gay found that the effect of that is like that of gravity on the tilted top – exactly enough to make it bend over and point down so elegantly.

All of which makes an already exciting game all the more interesting to those who like to wonder why the things we have seen so often actually work out the way they do.