Plenty of science in football

We are living in the age of COVID-19 and its impacts on what we consider normal. This is true of so many aspects of our lives, from work to family to play. It is readily apparent for large commercial sports.

We have hockey in July; baseball shortened to a 62 game season; and basketball finishing their season in August with a win by the Lakers. The CFL canceled its season on Aug. 17, but the NFL, of all the major sports leagues, is attempting to play a normal season – albeit with way fewer fans in attendance. And while the world has changed, the science underlying sports hasn’t.

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The physics of football is not anywhere near as well developed as it is for other sports, such as baseball or hockey. In part, this is because football is a bit more like organized mayhem than an orderly progression of plays. Yes, each play is drawn up beforehand and yes, each player knows his part. But as soon as the ball is snapped, everything is left to chance and random variables. It is hard to analyze such a situation.

But some aspects of the game do lend themselves to simple analysis. In particular, the passing and kicking game can be examined from the point of view of aerodynamics. After all, for the brief seconds when the ball is in the air, no one is touching it and the laws of physics are followed without interference.

These simpler aspects of the game have to do with the equations of motion. Knowing, for example, the hang time of a punt instantly tells you the height the ball reached. The equations of physics relate the height of a punt to the acceleration due to gravity and the square of half of the hang time. (It is the square of only half the hang time because the ball spends an equal amount of time going up as coming down.)

Consider, however, the simple act of throwing a forward pass. Not the easiest thing to do. Catching one isn't that easy either. This is why good quarterbacks and receivers are admired for their skill.

Among other things, both quarterback and receiver can be moving relative to one another when the pass is thrown and when it is caught. This makes the whole process an exercise in vector analysis. How the mind does this is an active area of neuroscience research and of interest to scientists exploring robotics.

The ideal pass is something called a perfect spiral. This is when the ball rotates around its long axis in a tight, rapid spin with the point of the ball following the arc of the throw exactly. Simple, really, except not from the point of view of the laws of physics.

The football acts as a spinning top or a gyroscope which, among other things, means it wants to keep the same plane of rotation the entire time. If you have ever held the axle of a spinning bicycle tire, you know the forces involved in trying to maintain the plane of rotation can be quite pronounced.

And yet, the football turns over in flight and the major axis follows a curve. The analysis of what is going on involves examining the torque induced by the displaced forces due to air resistance as the ball moves through the air. In essence, nose on, a football has symmetrical air resistance. But as it follows its arc, its nose moves to one side - it wobbles - thereby increasing the air resistance on the opposite side leading to drag. which torques the ball back into a proper flight path.

Throwing a perfect spiral is much more complicated than someone like Russell Wilson makes it seem! Indeed, this is why perfect spirals usually only occur when the quarterback has time to set his feet before the throw.

Interestingly enough, since almost every ball is thrown with spin, this can actually work against making a ball catchable. Unlike in baseball where the absence of spin generates a knuckle ball, a football without spin wobbles less than a badly thrown spinning ball. The reason is due to the precession of the spinning ball about the axis of flight, which can make the ball wobble quite rapidly, significantly decreasing the chances of a receiver being able to catch it. 

Of course, the science of football involves more than just physics. New chemical compounds, for example, have made for lighter stronger pads and helmets. Nutritional science has made for stronger and fitter athletes. And sports psychology manages to get everyone through the game.

With at least the NFL season in full swing, have some fun and watch a little science in action this weekend.

Or tune in to New Zealand rugby where they have fans in the stands!

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