We engineers aren’t known for our impressive physical coordination, but we are known to be good at math. So instead of learning how to throw a perfect spiral, let’s see if we can understand the physics behind a perfect football throw.
The physics behind football
There are a few principles in a flying football, like gyroscopic precession and parabolic motion. Looking back to some basic physics classes, we can understand that the way a ball flies depends on the launch angle and the speed it is thrown at. However, you can throw a football as hard as you want, that doesn’t guarantee that it will fly in a perfect spiral. In order to get a football to fly perfectly, we have to be a little more concerned with inducing gyroscopic precession.
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Precession has to do with the change of an object’s rotational axis when subjected to an outside torque, and it is crucial to a quarterback’s success. A good spiral spins at about 600 rpm or the equivalent of a cd in a cd player. As the football spins, it engages in gyroscopic motion.
The core principle of gyroscopes is that it takes a lot of outside force to interrupt their motion. When a spinning football flies through the air, gravity pulls the nose of the football downward in a parabolic shape. The same principles of all parabolic motion act on the football, but because it is spinning, it becomes much more stable and resistant to external forces.
Due to the gyroscopic effects of a spinning football, the way the ball behaves in the air actually varies based on whether the quarterback is right or left-handed. A ball thrown by a right-handed quarterback will curve slightly to the right, and one thrown by a left-handed quarterback would do just the opposite. Understanding this is essential to throwing an accurate pass.
What it takes to throw a spiral
Now, adding more spin to the ball isn’t all that throwing a good spiral needs. A faster-spinning ball will take up more proportion of the imparted energy to continue spinning than to continue moving forward. This means that quarterbacks can actually lose yardage when they impart more spin to a ball. It’s all about finding a happy medium. The ball needs the necessary amount of spin to attain proper gyroscopic motion, while also maximizing the forward velocity to maximize range.
The launch angle is another fairly simple aspect of a football pass, but one that is essential to mastering the game. Like any other trajectory, the maximum distance can be achieved with a launch angle of 45 degrees. At higher than 45, height will be maximized, and at lower angles, the ball will likely not travel as far as you need it to.
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The spin of a football is all about accuracy, the more consistently you can control a football’s spin, the better you will be at throwing the perfect, and accurate, spiral.
Throwing a perfect football may be easy to understand from a mathematics and physics perspective, but mastering the art is a completely different challenge. If you were to give any random physics student a problem involving a quarterback and a running receiver, it would likely be one of the most difficult parabolic motion problems they ever completed. Yet, good quarterbacks can perfectly take into account launch angle, velocity, and spin to perfectly place a football in the hands of a receiver down the field.