Pune: David Beckham’s precision bends, Roberto Carlos’s power-packed long-rangers or Lionel Messi and Cristiano Ronaldo’s swirling free kicks have left football fans and experts mesmerised for years. But researchers say there’s science behind such magical strikes that often seem to defy logic.Behind every such strike lies an invisible contest between the football and the air around it, a contest governed by laws of physics that scientists in Indian laboratories are decoding.“The science is similar to how a cricket ball spins because of air travelling at different velocity on a smooth surface compared to on a rough surface. When the surface of the ball is smooth, air travels faster compared to when the surface is rough. That is how the leather ball swings towards the shiny surface,” said Mayuresh Surnis, assistant professor in the department of physics, Indian Institute of Science Education and Research (IISER), Bhopal.“Similarly, a football has ridges. If a player hits the ball at an angle, it will spin while in the air. This will give it a drift because the part going with the direction of the motion will have a higher air resistance compared to the part going in the opposite direction. This will lead to the ball dipping down if it is spinning with a horizontal axis and sideways if it’s spinning along a vertical axis,” he explained.Advances in artificial intelligence are also helping researchers study these movements in greater detail. At IIT Ropar, researchers have developed an AI-based system that estimates the spin of a moving ball using ordinary video footage. According to Dr Mukesh K Saini, associate professor and co-principal Investigator at ANNAM.AI, understanding spin could transform both sports research and coaching. ANNAM.AI is the artificial intelligence model of IIT Ropar.“Our work shows that spin has a significant influence on a ball’s trajectory. AI can now estimate that spin from video, allowing us to study how different kicks behave. Such tools could eventually help coaches analyse technique, improve player training and better understand why certain shots move the way they do,” Saini said.MS Santhanam, professor with the physics department at IISER-Pune, said, “The moment a football is kicked into the air, it becomes an aerodynamic projectile. Its flight is determined by the interaction between gravity and fluid dynamics.”He said, “The flight of a football is decided long before it reaches the goal. As the ball moves through the air, a thin layer of air clings to its surface. The behaviour of this layer determines whether the ball travels smoothly, slows down, curves or becomes unstable.”According to him, the aerodynamics of a football depends on several factors, including its speed, the amount of spin imparted by the player, and the design of the ball. “The seams and textured surface are not merely cosmetic. They are designed to induce controlled turbulence in the airflow. This reduces drag, allowing the ball to travel further while maintaining a more predictable flight.”The science behind modern football design has been explored extensively by researchers. Studies published in Journal of Sports Sciences and later wind tunnel experiments have shown that the number of panels, seam patterns and surface texture significantly influence airflow around the ball, affecting its speed, stability and overall flight. The findings have helped explain why successive generations of FIFA match balls have behaved differently under identical playing conditions.While engineers design footballs to fly consistently, elite footballers know exactly how to make them do the unexpected. Senior sports biomechanist Vishwas Sharma said, “The engineering gives players a stable platform. What separates elite footballers is their ability to deliberately manipulate that stability by changing how they strike the ball.”Explaining the science behind the famous curls, Gopal Dixit, professor in the physics department at IIT-Bombay, said players intentionally strike the ball away from its centre to generate rapid spin.“The spectacular trajectories that captivate football fans are elegant demonstrations of Bernoulli’s principle and the Magnus effect. As the spinning ball moves through the air, it drags a thin layer of air along its surface. One side accelerates the airflow while the other slows it down, creating a pressure imbalance. That imbalance generates an aerodynamic force which bends the ball gracefully through the air,” said Dixit.In fluid dynamics, Bernoulli’s principle states that an increase in the speed of a fluid occurs simultaneously with a decrease in pressure or a decrease in the fluid’s potential energy. The Magnus effect refers to the phenomenon where a rotating object in a flowing fluid experiences a force perpendicular to the direction of its motion, resulting from differences in fluid velocity and pressure created by the object’s rotation.Few shots have fascinated football fans more than Ronaldo’s famous knuckleball free kicks, where the ball appears to wobble, dip and suddenly change direction. “The knuckleball is almost the opposite of a curling free kick. The ball is struck with very little spin. Without that stabilising rotation, the airflow keeps shifting around the surface, making its flight highly unpredictable,” Dixit said.He said the airflow alternates unpredictably between smooth and turbulent states, creating constantly shifting pockets of pressure around the football. “Without the stabilising Magnus force, those changing pressure zones make the ball flutter and wobble in ways that are extremely difficult for goalkeepers to anticipate.”Scientists have spent years trying to understand this phenomenon. AN Hussain, fluid physicist from Indian Association of Physics, said, “Laboratory experiments using wind tunnels, programmable ball-launching systems and high-speed cameras have confirmed that even small changes in airflow around a low-spin football can dramatically alter its trajectory, making knuckleball shots among the most unpredictable in the sport.”
