Only a handful of researchers have studied why an American football flies in such a unique trajectory, weaving through the air with remarkable precision, but also deflecting, wobbling and even tumbling as it hurtles downward. Now, ballistics experts at Stevens Institute of Technology have, for the first time, applied their understanding of artillery shells to explain this unique motion, creating the most accurate model yet of a balloon’s flight. spiral football.
“When a quarterback makes a good spiral pass, the trajectory of the ball is remarkably similar to that of an artillery shell or a bullet, and the Army has invested enormous resources in the study of how these projectiles fly,” explained John Dzielski, a Stevens researcher. professor and mechanical engineer whose work is reported in Open Journal of Engineering from the American Society of Mechanical Engineers. “By using well-understood ballistic equations, we were able to model the flight of a soccer ball more accurately than ever before.”
In fact, says Dzielski, while the ballistic equations themselves aren’t terribly complex, the motions they predict can be. The equations contain many terms that represent all the ways air can affect the motion of a shell. The first challenge was to consider each variable in turn to determine which ones are important when used in a new or different context.
Dzielski and co-author Mark Blackburn, principal investigator at Stevens, first took a comprehensive approach — modeling everything from a quarterback’s laterality to the effect of crosswinds to impact of the Earth’s rotation – then derived equations that removed the factors. it did not substantially influence the flight path of a soccer ball. For example, during a 60 meter pass, the Earth’s rotation changes the end point of the pass by only four inches. “It turns out that the Earth’s rotation doesn’t have much of an effect on a football pass – but at least now we know that for sure,” Dzielski said.
Modeling the flight of a soccer ball sheds light on what separates good passes from bad ones. Dzielski and his colleagues not only showed that a spiral pass can oscillate at a slow rate or a fast rate (or a combination of both), but were also the first to calculate what those frequencies are for a soccer ball. . If the ball wobbles slowly, it was successfully thrown. If he wobbles quickly, the quarterback twisted his wrist (like turning a screwdriver) or pushed himself to the side when the ball was released. The wrist may have twisted because the quarterback was hit.
“Quarterbacks and coaches already know this intuitively, but we were able to describe the physics on the job,” Dzielski said.
Another, more surprising finding, was that the Magnus effect, which causes a spinning baseball to slide or deflect due to changes in atmospheric pressure, has remarkably little effect on a spinning soccer ball. A soccer ball rotates along the wrong axis to trigger the Magnus Effect, so any deviation from the flight path must come from a different source, such as the lift created when a ball tilts in the air , explained Dzielski. “Many people think that soccer balls move left or right because of the Magnus effect, but that’s not the case at all. The effect of the Magnus force is about twice the ‘effect of the Earth’s rotation,’ he said.
Moreover, Dzielski and Blackburn showed, for the first time, that this lurch is intimately related to why the ball ends up nose-down at the end of the pass when thrown.
Although Dzielski and Blackburn’s work represents the most accurate model of a soccer ball’s flight path to date, Dzielski warned that more work is still needed. Because a soccer ball spins and tumbles as it moves, it is nearly impossible to use wind tunnel studies to accurately record the aerodynamics of a moving soccer ball. “That means we don’t have good data yet to feed our model, so it’s impossible to create an accurate simulation,” he said.
In the coming months, Dzielski hopes to find funding for instruments that can capture aerodynamic data from a free-flying soccer ball in real-world conditions, not just in wind tunnels. “It’s the only way to get the kind of data we need,” he said. “Until then, a truly precise – and precise – way of modeling the trajectory of a soccer ball will remain out of reach.