Football Physics

Each and every sport is based on applied physics. Many physical laws come into play. By precisely controlling these laws, we can efficiently and effectively play all types of sports. Each sport has its own underlying physics, but in most cases, Newtonian mechanics has a crucial role. In this article, we will deep dive into the physics of football. Gravity, friction, drag, aerodynamics, velocity, moment, etc., are the main factors that are present when playing football. We know that kicking a football causes it to roll or slide across the ground. Have you ever thought about how this happens? What is necessary to force the ball to move more quickly? What is the difference between shooting and nudging a ball? What happens when you stop and hold a fast-moving ball? Many physical constraints come together to produce the above results.

Physics behind Football

When you kick a football, sometimes you might see the ball travelling in a weird trajectory. Lord Rayleigh gave the first detailed explanation of lateral motion and deflection of spinning bodies. He explained these effects using the works of physicist Gustav Magnus. Magnus conducted the examination of the deflection of bullets and spinning shells. His research can be directly applied to the movement of balls. The basic mechanism of a curving and spinning ball in football is identical to all other ball games like cricket, baseball, tennis, golf, volleyball, and table tennis.

Magnus Effect in Football

The Magnus effect generates a curve on the football during the motion. When the ball is spinning in mid-air, the frictional force between the ball’s surface and the air reacts to the spinning ball’s direction. When the ball has topspin, the air velocity at the top of the football becomes less than the air velocity at the lowest part of the ball – the tangential velocity of the top part of the ball functions in the opposite direction to the airflow. On the flip side, the tangential velocity at the ball’s bottom side functions in the exact direction of the airflow. As the air velocity at the ball’s top part is much less than the velocity at the ball’s bottom section, the top of the ball encounters a greater pressure when compared to the bottom of the spinning ball. It causes a downward force called the Magnus effect.

This spinning ball effect is always present when a player kicks the ball at the right or left of its centre; the football spins in a counterclockwise or clockwise direction. Depending on the direction of the spin, the Magnus force acts in the leftward or rightward direction, forcing the ball to curve left or right.

Read More: Magnus Effect

The video explains the basics of the Magnus effect

Mass and Weight in Football

In physics, the weight of a football is the force exerted on a body by the Earth’s gravity. However, mass is the amount of matter inside the ball. The mass of the ball does not change regardless of the nature of its location or position and the strength of the gravitational force.

The weight of the ball and players play a crucial role in the movement of the ball. If the ball is heavy, it’s comparatively much more difficult to kick and move the ball. The force of the kick is also influenced by the weight of the player involved in the action. Thus, it is the culmination of weights of both the player and ball that results in the overall nature of the ball’s speed. However, if the players’ weight exceeds the structural capacity of their bodies, the degree of movement could be drastically reduced. As football is a game of both power and movement, optimal weight is required to play the game effectively and efficiently.

The video explains the mechanics behind football throw-ins

Velocity in Football

Velocity is the speed of a body in a distinct direction. The speed and the direction determine the efficiency of a pass or shoot. So, if players are not aware of the ball’s velocity, they will not be able to control and manoeuvre the ball precisely. Players should know the velocity when they kick the ball. Otherwise, they will not be able to pass or place the ball as intended accurately. Especially in the case of long passes and through passes, players have to predetermine the ideal speed and direction. Even if a player wants to stop a ball, he has to be aware of the velocity to balance out the force exerted when the ball touches the body.

The video explains the mechanics behind lob passes and bullet passes

Friction in Football

Friction is the force that opposes the rolling or sliding of one body over another. In football, frictional forces oppose the movement of the ball when it is rolling or sliding during the play. This is due to the fact that these balls move against the surface of the ground generating a resisting force (surface friction) which considerably slows down the ball. Players have to be very careful with their ball technique to reduce friction. In some cases, if they want to slow down the ball, then they can make use of friction.

Momentum in Football

Momentum is a body’s velocity times its mass. It can be stated as “mass in motion”. Every single time a player strikes the ball, the body transfers varied ranges of momentum to the ball. When players run and kick the ball, the combination of mass and velocity gets transferred to the ball’s movement. The higher the momentum, the faster the ball moves. In the case of receiving a ball, the ball’s momentum is reduced meticulously by transferring the excess to the receiver’s body. (Newton’s second law of motion).

Drag in Football

Drag is generated when the ball moves in the air. When it travels through the air, depending on the atmospheric density, the air pushes back at the ball. This slows down the speed of the football. Drag is also the main reason why football doesn’t move in an ideal parabola trajectory.

Reducing drag is a crucial aspect of football. It can be effectively cancelled by generating enough spin. As the ball begins to spin, the Magnus effect will start to activate. This dramatically reduces the drag force on the ball.

Gravity in Football

Each and everything falls under the influence of gravity. Therefore every sport is heavily influenced by the intricacies of gravitational force. Every movement is controlled by the Earth’s gravity. Acceleration due to gravity plays a crucial role when a ball moves in a vertical, horizontal, diagonal, or any other direction. Depending on the direction and angle of the movement with respect to the playing ground, gravity drives or slows down the ball’s motion. When a player kicks or throws a ball, the first force that acts against the ball’s motion is gravity. When the ball starts to rise, gravity continuously pushes down the ball along with the air resistance.

The video explains the application of centre of gravity in football

Roberto Carlos Freekick

One of the fundamental activities in football is kicking the ball. With different striking techniques, players can generate various types of trajectories and speeds. Now let’s examine arguably the best freekick ever taken in the history of international football. In 1997, Roberto Carlos produced an impossible free kick 35m away from the goal post.

The Brazilian kicked the ball with his left foot’s outside part. This generated an anticlockwise spin on the ball. The weather was on the dry side. This enhanced the moving ball’s spin to many folds than normal conditions. He should have kicked the ball with an approximate speed of over 70 mph. The airflow over the ball was tempestuous. Therefore, at that moment, the ball encountered relatively less drag along the trajectory. Around the wall of defenders, the ball’s speed decreased considerably and entered the laminar flow state. In this state, the drag increased significantly, and the ball slowed down further. This created lateral Magnus force that enabled the ball to bend towards the goal post. The rate of spin didn’t decrease, and the drag coefficient increased. This produced even more lateral movement and forced the ball to bend even more. In the end, as the speed continued to decrease, the ball continued to bend further. This was most probably due to the rise in the lift coefficient. Overall, the ball took a bizarre trajectory that defied the conventional movement of football. This freekick is a perfect culmination of all physical phenomena mentioned in this article.

Watch the video and learn more about Magnus effect in football

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