- [Narrator] The perfect football pass, a thing of beauty, and bewilderment.
The way the football travels mid-air baffled physicist for years.
- If you're in the physicist world, you'd expect the football to travel like this and come down.
When you watch a long pass from a talented quarterback, you can just see the football just travel like that.
- [Narrator] So why does the nose of the football go from pointing upward to rotating downward, when most things stay the same orientation as they move through the air?
There are two key players involved, gravity and angular momentum.
So what is angular momentum?
First, it'll help to understand momentum.
You're probably used to experiencing linear momentum.
Imagine you're a passenger in a car traveling at 40 miles per hour and the driver suddenly brakes, but you continue moving forward.
That's what seat belts are for.
- A body of motion tends to stay in motion unless acted on by a force, and that's conservation of momentum.
- [Narrator] Then there's angular momentum, which is when an object with mass is spinning.
You can see this property in action when an ice skater speeds up when they pull their arms in.
In football, conservation of angular momentum is the reason why the ball changes orientation while it spins through the air.
Let's compare a football spinning vertically on a flat surface to a spinning top.
- The top of the top will describe a circular orbit around a vertical axis.
The vertical axis is set up by the force of gravity.
Gravity is trying to pull the top over, but the top refuses to fall over.
To conserve angular momentum, it processes in a circle.
- [Narrator] A football acts kind of like a top, a symmetrical top.
- Now the axis about which the ball rotates is not caused by gravity.
In the case of the football, it's processing around the onrushing force of air that the ball experiences.
- [Narrator] The force of the air pushes on the ball causing it to wobble around its spinning axis, and this wobble eventually pushes the nose down.
- [Timothy] Gravity absolutely acts on the football, but its effect is to cause the ball to go up and then come down in that curved parabolic trajectory.
- [Narrator] Put them all together and you get that beautiful pass.
But to gain the most amount of yards in the shortest amount of time, the quarterback needs to keep a lot of things in mind.
- The thing I look for in a quarterback is a lot of intelligence and understanding.
After that, it's accuracy with the timing to get the ball out and just awareness.
- [Narrator] And the spin of the ball is crucial to getting it to go the distance.
- If you don't throw a spiral, that thing is gonna flutter.
We call those ducks.
The ball starts to fluter, doesn't get velocity, doesn't get distance, and those end up getting intercepted by the defenders.
- [Narrator] Here's how they get that perfect spiral.
- So your firm grip must come from these fingers and the other last two in the back, that's kinda more so for the guidance.
I also try to have a gap right here.
- [Shane] From that, it's all about where your arm is going and then the snap of your wrist.
- [Narrator] And they have to release the ball quickly.
In those seconds- - Once the ball is snapped, the quarterback is focused on several different things.
So we're catching the ball.
We're also scanning what's going on in front of us.
We're backing up away from the line.
We're actually flipping the ball to put the laces on our hand.
- [Narrator] Physics may be an integral part of football, but to players- - It's all about time and practice and repetition.
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