The Physics Behind Ball Design

Each sport is governed by different sets of rules, and those that use balls each have different specifications for their equipment. The baseball, basketball, golf ball and football are all essentially by-products of physics. Sports is big business, and hundreds of millions of dollars may hang in the balance when we are dealing with a few obscure physical laws. For example, at the recent World Cup soccer championship, the shape of the pieces making up the surface of the soccer ball was changed by the manufacturer, leading to charges that some teams received an edge over others.

Lots of sports equipment designers and even the franchises themselves have consulted with my colleagues to gain a better insight into the science of the game. You may be wondering why the sports industry would want to pick the brain of a physicist; well, let’s take baseball for example. We all know that when you look at a baseball, it has threading woven through the leather of the ball in a particular shape. The threads of each section meet at the seam of the opposite thread on the other side of the cut. Tests, including time-lapse photography and wind-tunnel technology, have allowed us to determine that these threads play a huge role in the success of the fastball, curveball and even the famed knuckleball. Basically it boils down to: The faster a ball spins as it slices through the atmosphere, the more stable it is from point A to B. Since a fastball spins very rapidly for example, it is very stable and this is widely due to the layout of the threading.

But let’s take a look at the knuckleball, which has been the topic of many a debate over the years. The movement on this pitch is caused by mini-vortices forming over the threaded/stitched seams which cause the ball to rapidly change it’s position in the air. The ball can change direction, corkscrew, appear to take a dive, flutter, dance or even curve in two opposite directions during it’s flight. The key to the knuckleball is the way that the pitcher holds the ball with his knuckles, releasing it straight out to completely avoid the normal rotational spin of a pitch. The immediate absence of the rotational spin causes an asymmetric drag that tends to deflect the trajectory towards the side of the stitches. This drag is essentially what gives the flight of the ball such an erratic motion on it’s way to the catcher’s mitt. This particular pitch is also very difficult to catch and some knuckleball pitchers have even required their own catchers.The art of a knuckleball:

Have you ever wondered exactly what’s inside of a baseball?

Now also, if you take a look at football. It’s true that the faster you throw your spiral, the better control you have over the delivery. The faster the spin, the greater reduction of eddy currents allowing it to slice through the atmosphere to deliver a touchdown. The mini-dimples on golf balls are also engineered to reduce eddy currents, allowing the ball to travel much further by reducing the drag on the ball as it flies through the air.

In 2006, a group of researchers at Arizona State University used a bit of aircraft science to try and design a better golf ball, which would be more efficient in all weather conditions, cost less and travel farther. One of the battery of tests they performed took 64 high-powered computers running for a full week to evaluate the flight of one ball under one set of conditions.

So, this just gives you an idea of the thought and ingenuity that goes into the designs of such equipment. Think about all of that the next time you throw a baseball, football or swing the golf club to hit that dimple-covered golf ball.