NFL great Jerry Rice found the football flies in a way that perplexes rocket scientists.
A football has a shape that mathematicians call a prolate spheroid. While that sounds like a weird word, prolate spheroid shapes happen in your everyday life as grapes, lemons, and watermelons. They are all longer in one direction than the other. This weird shape of the football means that it cannot be thrown like a baseball. The only way for a football to stably travel long distances is if thrown with a spin.
When a quarterback throws a football, the football spins more than 600 times in a minute, which is as fast as a CD spinning in a CD player. This spin does a few things. First, it stabilizes the ball. Without the spin, the ball would flop over. The second thing that the spin does is it creates new complicated behaviors too.
The spin creates what scientists called gyroscopic torque. This sounds like a strange thing, but gyroscopic torque happens when you ride a bike. When the wheels spin, you keep upright. However, as soon as the wheels slow down, you lose your balance. The same happens with the football. The spin keeps the football’s nose from falling down just like the wheels of the bike.
However, the spin also allows footballs to do something a bit strange. It acts like a toy gyroscope. If you ever take a spinning gyroscope toy and push it, the toy will mysteriously move on its own in another direction. This same thing happens to a football. A football spins and points its nose up, but gravity pushes its nose down as the football comes back to earth. So the football moves on its own and points sideways. (Next time you are watching a game, notice that the football’s nose is a bit to the side. That’s gyroscopic torque in action!)
So why is this a big deal? If a football is pointing sideways, then this means that a ball can be off its target by a few yards. Quarterbacks must account for this shift when they throw. Many QBs know about this instinctively and do this automatically. But, new QBs have to learn this.
Interestingly, a football spins differently if a quarterback is right-handed or left- handed. When a right-handed quarterback throws the ball, the ball spins clockwise. This means that the ball shifts a bit to the right. A left-handed quarterback throws the ball with a counter-clockwise spin, so the ball veers to the left. A ball will look very different to a wide receiver depending if a quarterback is right handed or left-handed. In fact, Jerry Rice, the great NFL wide receiver, confirmed that the ball looks different. Rice saw something that perplexed professors for years.
As one can see, the football’s tight spiral is poetry in motion, but it is also science in action.
Next Generation Science Standard NGSS PS2.C
The Physics of Football by Timothy Gay (Affiliate Link)
Newton’s Football by St. John and Ramirez (Affiliate Link)