# Football and physics? Yep, it's a thing.

| Judy Berthiaume

When football fans gather to watch the Super Bowl Sunday most of them won’t really care about the actual game.

After all, just two — or 6.25 percent — of the 32 NFL teams are still vying to be the 2017 champions.

Still an expected 100 million+ people around the globe will gather with family and friends to watch Sunday’s game between the Atlanta Falcons and the New England Patriots.

Why?

For many, it’s all about the commercials. With 30-second ads costing up to \$5 million, advertisers will roll out their most creative work as they try to score points with the huge viewing audience.

Others are in it for the guacamole, chicken wings and beer. Last year Super Bowl spending topped \$15.5 million, according to the National Retail Federation.

And still others, like Dr. Erik Hendrickson, tune in for the fascinating physics that are on display during every play.

Huh?

Yep, football and physics is a thing.

Before you dub Erik the most boring Super Bowl party guest ever, give the UW-Eau Claire physics professor a chance to break down the science behind those impossible-to-make passes or bone-crushing hits.

You might just learn something … and find yourself watching Sunday’s big game in a whole new way.

How do quarterbacks make those seemingly impossible throws?

Projectile motion is the path that a thrown or kicked ball follows through the air.  It looks like an arc, especially when air resistance is kept to a minimum.

If we know the initial speed of the ball and the angle that it’s thrown or kicked, the math can tell us exactly where the ball will land, precisely how long the ball will be in the air, and how fast and in what direction the ball will be moving when it’s caught.

While the players are probably not using this mathematical function to calculate these variables in their heads while throwing or catching the football during a game, they’ve watched and analyzed hundreds of hours of film showing the throwing and kicking tendencies of their opponents, which includes studying the release angles and initial speeds.

In other words, they’ve definitely done their physics homework.

Why does the spiral matter so much?

To keep air resistance to a minimum and to keep the predictability high, quarterbacks and kickers want the ball to travel with a tight spiral.

The physics behind this type of motion is angular momentum.

Once an object is initially set into a spinning motion, it will want to continue to spin in the same orientation.

Most people realize that it’s easier to keep a bicycle upright once it is already moving. This is the same physics principle: once the bike wheel is spinning in a vertical circle, it does not want to change its orientation, which means it doesn’t want to fall over.

This also is the reason that the inside of the long barrel of a rifle has rifling, or grooves that rotate as you move down the barrel.  This causes the bullet to be spinning extremely fast as it comes out of the rifle, just like a well thrown football.

In the case of a football, you want the nose of the ball pointing down field.

Having the pointy nose of the football always in front decreases the air resistance as it moves through the air quickly and increases the predictability of the path that it takes.

What’s the physics behind those bone-jarring tackles … or missed tackles?

If a large object is moving quickly in a straight line, it wants to keep moving in the same direction at the same speed.

So, when you see fast running backs carrying the football, they have a large linear momentum in the forward direction.

Of course, the defense would like to stop the running back’s forward motion, or momentum.

Often defensive linemen and linebackers are much larger, but also slower, than the running backs.

So how can they stop the RB?

Even with their slower speed, their larger mass means that they can generate just as much or even more momentum in the opposite direction as the RB.

So when the collision occurs, you can always tell who had the most momentum.

Sometimes the RB basically runs over the defender or is able to fall forward to gain yardage, and in this case the RB wins the momentum game.

Other times, the RB gets sent hurtling backwards from the hit, and it’s the defender who won the momentum battle.

How does the field surface affect the players?

It comes down to friction.

The surface of every football field is different, especially today with artificial turf or the heated ground beneath Lambeau Field.

So for every game, the players need special and specific shoes so they can use the friction between their feet and the turf to their advantage.

We all know what’s it’s like to try to walk on an icy sidewalk without falling down.

Think about being at a standstill and then trying to accelerate to your top speed as fast as you can.  If your shoes do not grip the ground very well, like on the icy sidewalk, it means there isn’t much friction between your shoes and the ground.

Football players want to increase this friction so they can speed up quickly — or generate more momentum —  and also to make sudden cuts in their motion, which allow them to evade tacklers or to shake loose from a defender’s pass coverage.

Sometimes after a touchdown pass you wonder how a player got so open. Then you see the replay where the wide receiver made a sharp cut and as the cornerback tried to follow the change in direction, he slipped and fell.

Many players bring multiple sets of shoes to each game — some have longer or shorter cleats on them, or even just a different pattern of cleats — since the condition of the field can change during a game.

Often you see players on the sidelines switching shoes between plays as they try to find the right amount of friction for them to play the game to their best ability.

With all the protective gear players wear, why are there still so many injuries?

During the violent collisions in a game, as the battle of momentum is waged at many different levels, the kinetic energy — the energy of motion — needs to be conserved.

One of the fundamental laws of physics is that you can’t create or destroy any energy.

The players eat lots of energy-filled food leading up to a game, and their powerful bodies transform this chemical energy during the game into kinetic energy, with the goal of moving the ball toward the end zone.

When a collision occurs, all of this kinetic energy seems to disappear, since no one is moving after the ball carrier has been tackled.

Of course, the energy can’t really disappear; it has to go somewhere, and much of it goes into the players’ bodies.

Since these players are large and strong, there is a lot of energy that gets deposited into their bodies during a collision.

This energy can cause serious injuries: torn ACLs, broken bones, concussions and more.

That’s why the players wear so much protective gear. The pads and helmets are designed to absorb much of this energy.

But even as the protective gear advances thanks to technology — materials science and nanotechnology are making gear stronger yet lighter, for example — the injuries keep coming.

The players keep getting stronger and faster, and the gear just can’t compensate enough.

So while the gear helps, there still is a need for new rules for protection, like you can’t use your helmet as a spear when tackling someone, you can’t hit the quarterback if they slide down, and no helmet-to-helmet contact.

The emerging research on the severity of the long-term damage that concussions can cause has led to a lot of physics research on how to create better helmets to prevent such injuries.

But we’re not there yet.

Anything else you want to say to those watching Sunday’s game?

Enjoy the football game and munchies, and have fun critiquing the commercials.

But pay attention to the physics going on through all the different aspects of the game.

All the things that make football so fun to watch — from the unpredictable bounce of a ball that changes the course of a game to the Hail Mary touchdown to the receiver eluding a defender — really are physics in action.