When the soccer video game FIFA 14 went on sale this week, it boasted a ball that, at long last, could sail smartly through the air. In earlier versions of the game, unless the ball was kicked long distance, it became undeniably “floaty,” soaring at an unrealistically linear path. A year ago, a team of engineers and animators at EA Sports (a division of Electronic Arts, Inc.) set out to get to the bottom of the problem. They conducted an intense audit of all the projectile physics code in the game in order to figure out which formulas were not working properly. After much research they found their drag coefficient was wrong.
The drag coefficient is coded into the game’s software to simulate air resistance, which greatly affects the pace at which an object rises and falls in the shape of a parabola. “The ball moves at its fastest velocity when it comes right off the foot, and air resistance immediately slows it down until it reaches its maximum height,” says John Eric Goff, Lynchburg College physicist and author of Gold Medal Physics: The Science of Sports. “The ball should then pick up speed on its way down.”
In previous FIFA versions the ball violated the laws of physics, accelerating and decelerating at a set rate unaffected by its initial velocity. “So if the ball was moving at 30 or 50 miles per hour, it was going to slow at the same rate as if it were moving at five miles per hour,” says Aaron McHardy, EA Sports senior gameplay producer. Thus, the ball would not slow quickly enough for a player to kick it with an accurate amount of force, and they were not able to kick the ball as hard as real-world players do.
The incorrect drag coefficient also affected the ball’s spin, which had major implications for its lateral trajectory and speed. As a spinning ball whips air off to one side, an equal amount of force, called the Magnus force, pushes that ball in the opposite direction (Newton’s third law). Because the drag coefficient was incorrect in previous FIFA versions, the Magnus force was also miscalculated, and the ball wasn’t spinning or curving accurately. “Once fixed, the ball would spin appropriately, and we got so much more variety in the curve,” McHardy says. The Gameplay Team had wanted for years to include dipping shots and low rising shots, and was able to do so in FIFA 14 directly because they fixed the air-resistance issue. “The ball now finally dips and swerves,” he adds, “and does all these things that we see in the real world.”
EA Sports’s FIFA was originally released in 1993 and has been released annually since. It has become one of the best selling video game franchises, selling over 100 million copies worldwide.