Understanding the physics of soccer may give players a competitive advantage.
As the 2018 World Cup heads into the quarterfinals, every goal counts and the pressure is on the world’s top scorers to perform.
Many factors are at play in determining which countries advance including points based on wins, losses or draws; total goals scored and goal differentials. The common denominator — goals.
But, how do players manage to score goals that seem impossible? How do players make the ball bend? Physics.
Physics Professor Yesim Darici explains there are several forces at play when a player kicks a ball and it’s all based on Newton’s laws of motion. We highly recommend you grab a soccer ball to do your own demo and follow along.
- Weight— A soccer ball weighs 1 pound. It’s that weight that keeps the ball on the ground. According to Newton’s first law,the ball will stay on the ground unless some force acts on it because an object at rest stays at rest unless acted upon. When the ball is kicked, its center of gravity shifts, thus sending the ball into motion. Simple, right?
- Drag— Newton’s second law — which basically says the acceleration of an object is dependent on its mass and the force you use to move it — totally explains a soccer ball’s drag. The strength of the drag force is affected by the shape and size of the object, its velocity and the density and stickiness of the air. Since a soccer ball is not smooth, its stitches in the seams affect its drag.
- Lift— When kicked, the soccer ball rotates on its axis. For example, if you kick a ball off-center with the side of your foot, it will rotate horizontally. It will bend. (For you non-soccer fans, it’s curving.) When kicked head-on with a toe, it rotates vertically up into the air and then down. In both scenarios, the ball is interacting with the movement of air around it. This is called the Magnus effect (more on that in a minute). For you Physics junkies, welcome to Newton’s third law — for every action, there is an equal and opposite reaction.
Now back to that Magnus effect. Physicist Idaykis Rodriguez with FIU’s STEM Transformation Institute, describes it as the force caused by the spinning of the ball which makes it bend.
“As the ball spins through the air, the air that’s going with the spin is going to move faster than the air that’s going against the spin,” Rodriguez said. “This difference in air around the ball makes it so there’s a pressure differential which creates a force in the direction of less pressure.”
But players don’t examine the forces of physics as they kick the ball. Instead, they learn what works through practice. Through drills, they learn if they kick with the tip of the foot, there is more force on the kick, but it’s less accurate. They see that although there is less force when the ball is kicked with the inside or outside of the foot, the kick is more accurate. At FIU, researchers call that active learning. It’s a tactic deployed in classrooms all across campus and pioneered by the STEM Transformation Institute.
Darici believes the players that understand the Magnus effect may be a step ahead. Knowing the ball will always behave a certain way depending on how it’s kicked and which part of the foot is used to kick it, can change the way a player approaches a kick.
“Kicking at the center of the ball with your toes will send it moving in a projectile path. Kicking any other area of the ball with inside or outside part of your feet will cause it to spin on its axis, and it makes ball’s trajectory bend,” Darici said. “The soccer players become famous with their bending skills and practice makes perfect, but knowledge is power. We may be looking at a possible research study looking at the importance of learning physics in soccer.”