This Sunday in Vancouver, thousands of people will gather to watch an impressive demonstration of momentum, mass, drag and other basic physics provided by highly trained specialists from Hamilton and Calgary. This scientific exposition is called “the Grey Cup.”
One interesting demonstration will be the forward pass. A football moving through the air has inertia–the universal tendency of objects in motion to remain in motion (and objects at rest to remain at rest). If not for gravity and air resistance, it would simply sail away in a straight line and never come down.
Gravity, however, pulls the ball down from the moment it leaves the quarterback’s hand. The quarterback’s goal is to balance the momentum he gives the ball with the rate at which gravity will pull it down, so that the ball descends at just the right moment to a point on the field occupied by a receiver. A long bomb is thrown both up into the air and very hard to maximize the distance it travels. A short bullet pass is thrown almost horizontally, because gravity has little time to work on it.
Aerodynamics comes into play during the pass, as well. A ball will travel further and straighter if it’s spinning around its long axis. If it’s not spinning, the air rushing up under its tip as it descends causes it to tumble, and it falls from the sky quickly. Spinning stabilizes a football through “angular momentum.” A spinning object resists having its axis tilted. That’s why it’s easier to balance on a fast-moving bicycle than a slow-moving one–the spinning wheels don’t want to be tipped.
Another demonstration of physics to watch for is the punt. Punters try to balance hang-time with distance. The higher the ball is kicked, the greater the hang time. Kicking the ball at a 45-degree angle gives you the greatest distance, but not much hang time; kicking the ball straight up in the air gives you the best hang time, but no distance at all. Most kickers choose something in between.
Many of the demonstrations Sunday will involve collisions between players. These collisions illustrate mass, momentum and friction.
When two football players collide, both players push each other, but the one with more mass is affected less. Fortunately for runners, who usually mass less than those trying to stop them, objects with greater mass are much harder to accelerate, and also resist changes in direction. That makes it possible for the lower-mass runners to dodge around their tacklers–sometimes.
To demonstrate Newton’s Third Law, “For every action there is an equal and opposite reaction,” players push the ground with a foot to change direction. The ground pushes back, forcing the player in the opposite direction.
Tacklers in Sunday’s scientific extravaganza will demonstrate one of three different aspects of physics each time they face a runner. The tackler’s goal is to rob the runner of his momentum. The first way to do that is to hit the runner directly. If he’s moving fast enough and weighs enough, he’ll win the ensuing transfer of momentum, absorbing the runner’s momentum and passing on enough momentum of his own to knock the runner down.
The second way to get rid of the runner’s momentum is to transfer it to the ground by knocking the runner’s feet out from under him.
The third method is to knock the runner out of bounds. This is often the easiest choice because, while a runner with a great deal of momentum is hard to stop, he’s easy to steer. A push redirects his momentum toward the sidelines. The runner has to push at the ground to correct his trajectory. If he’s close to the sidelines, he probably doesn’t have time–and ends up transferring his momentum to a photographer, cheerleader or TV camera.
To protect themselves from the effects of the sudden deceleration brought on by such transfers of momentum, Sunday’s scientific experts will wear helmets and pads. Both prolong deceleration to minimize the forces involved, and spread the forces that remain over a lot of skin, minimizing tissue damage. Prolonging deceleration is particularly important to the skull, because the brain moves somewhat independently of it. If the skull stops too suddenly, the brain can slosh forward, causing concussion (or worse). Slowing deceleration minimizes that sloshing.
Which is not to say that a lot of brains won’t be getting sloshed Sunday in Vancouver, as other highly trained specialists conduct their own demonstration of the effects of ethanol on the human nervous system, but that’s a topic for another column.