Introduction
The basic principle of soccer is rather simple: two teams, composed of eleven players each, compete on a rectangular court for control of a spherical ball, with the objective of kicking it into the opposite teams’ goal. The history of soccer goes back to the 2nd and 3rd centuries BC, as evidence of the sport being played in ancient China during those periods has been found. In modern times, soccer is undoubtedly one of the most popular sports in the world, if not the most prevalent, particularly in Europe and the Americas. According to Fifa, the 2014 World Cup Final drew in an estimate of 1 billion viewers.
Though the popularity of soccer continues to rise, knowledge of the laws of physics that describe the game is not so widespread. In consideration, this paper will analyze some of these laws, as this will give the reader a more profound understanding of soccer. Furthermore, soccer players that comprehend the basic physics behind soccer are more likely to have superior tactics in the field. Firstly, Newton’s First Law of Motion, commonly referred to as the Law of Inertia, demonstrates why a ball begins or ends motion; the concept of Momentum can aid in the understanding of how players influence the ball’s movement’s impulse and direction; moreover, the Magnus Effect can help in the prediction of a ball’s trajectory.
Newton’s First Law of Motion – Law of Inertia
According to Encyclopedia Britannica, Newton’s First Law of Motion states that “if a body is at rest or moving at a constant speed in a straight line, it will remain at rest or keep moving in a straight line at constant speed unless it is acted upon by a force”. In other words, unless acted upon by an unbalanced force, bodies in rest stay in rest, and bodies in motion stay in motion.
Applied to soccer, this law explains why a ball that has been placed on the grass remains statics until a player kicks it. Conversely, once the ball has been kicked it continues motion but gradually slows down as forces opposite to its movement, such as friction, gravity, wind, or another player’s kick act upon it until it completely stops or changes direction.
Momentum
Physics Classroom defines momentum as the quantity of motion an object has. It can also be defined as “mass in motion”, and it is dependent on two variables: mass and velocity. Momentum is denoted with the lower case letter p and the equation that describes it is as follows:
p=m*a
In this equation, p= momentum; m = mass and a = acceleration.
The resulting units for this variable would be the product of mass unites by velocity units. The most common resulting unit is kg*ms. Momentum is defined as a vector, thus being composed of both magnitude and direction. In this regard, the linear momentum components in each direction
(x, y and z) are: px=m*vx, py=m*vy and pz=m*vz. A related concept is impulse, which defines the change in momentum.
Dr. Garty explains how the concept of momentum applies to soccer. When a player kicks a ball, it provides it with momentum that drives it in the direction of the force applied. Moreover, players slow down the ball’s momentum as they manipulate it with their feet to maneuver through the court or pass it to another player. By slowing the ball’s momentum, the player has better control of the ball. The friction created by the contact between the ball and the grass also similarly reduces momentum.
The Magnus Effect
The Oxford Dictionaries define the Magnus Effect or Magnus Force as “the force exerted on a rapidly spinning cylinder or sphere moving through air or another fluid in a direction at an angle to the axis of spin”. Though the understanding of the Magnus Effect has several applications, the most widely known is the curved trajectory of balls in the air, particularly in soccer.
The Weizmann Institute of Science contends that when a ball is kicked at its side and towards the bottom, it will tend to rise and spin on its own axis, and will continue to do so until friction slows it down and the spinning motion changes its direction, as air moves faster on one side. In this sense, it can be understood that the ball will move on a straight line that follows the direction of the kick until it slows down enough for the Magnus Effect to occur. The intensity of the curl depends on the ball’s velocity, as it will tend to curve more with slower movement.
The curved deviation occurs because as the ball moves through the air with a spinning motion, one of its sides collides with passing air which forces it to decelerate and creates an area of high pressure; conversely, on the other side, the boundary air moves faster as it has the same direction of the surrounding air, which creates an area of low pressure. This differential pressure is what causes the ball’s trajectory to curve (Human Kinetics). Figure 1 illustrates the Magnus Effect.
Figure 1.- Magnus Effect
Source: Kunz, Josh
Figure 2 illustrates the deviations of the ball caused by it being kicked in different angles or sides. As can be seen in the image, when a ball is kicked right of center the Magnus Effect will deviate the ball towards the left, and vice versa.
Figure 2.- Deviation effect
Source: Real World Physics
According to Real World Physics, when soccer players are aware of this effect, they can successfully use it as a tactic to confuse their opponents by deviating the ball a few feet from their apparent trajectory. Moreover, as the Magnus Effect can be applied in any direction, players can create backspins, topspins and sidespins.
Conclusion
Soccer players that comprehend the physical laws that apply to the game of soccer, particularly regarding ball force and trajectory, are more likely to perform superiorly in the field. After analyzing these laws, it is clear that the previous statement is correct.
As explained, Newton’s Law of Inertia applies to any body either in movement or at rest, and indicates its tendency to maintain their state unless being subject of an unbalanced force. Momentum is a concept that describes bodies in motion, and is dependent on mass and acceleration. Soccer players can either increase the velocity or slower a ball’s momentum to manipulate it for different purposes. Lastly, the Magnum Effect explains how balls that appear to be moving in a straight line can suddenly change their trajectory by deviating a few feet from their apparent path. This is a particularly useful tactic, as curved balls can confuse goalkeepers or other players.
Though this paper can be extended to explain how other laws which are intrinsically related to these ones apply to soccer, including all of Newton’s Laws of Motion. However, the ones that have been described are sufficient to expand common individual’s knowledge on the sport.
References
Brown, Shael. "The Physics of Kicking a Soccer Ball." n.d. Web.
Encyclopedia Britannica. "Newton’s laws of motion." n.d. Encyclopedia Britannica. Web. 18 June 2016.
FIFA. "2014 FIFA World Cup™ reached 3.2 billion viewers, one billion watched final." 16 December 2015. FIFA. Web. 18 June 2016.
Garty, Erez. "The Physics behind Soccer Kicks." 02 April 2015. Weizmann Institute of Science. Web. 18 June 2016.
Human Kinetics. "Magnus effect." n.d. Human Kinetics. Web. 18 June 2016.
Kunz, Josh. "The Physics of Bending a Soccer Shot." 2006. Physics 211. Web. 18 June 2016.
Oxford Dictionaries. "The Magnus Effect." 2016. Oxford Dictionaries. Web. 18 June 2016.
Physics Classroom. "Momentum and Impulse Connection." n.d. Physics Classroom. Web. 18 June 2016.
Real World Physics. "The Physics Of Soccer." n.d. Real World Physics. Web. 18 June 2016.
