# Physics of Soccer

Physics of the Ball How and where you kick the ball is the most important aspect within the game of soccer. Lets say you kick the ball perfectly giving it no rotation (or spin), this means that you have given the ball a velocity (v) and an initial angular speed of zero. When the ball comes into contact with the ground it will begin to spin because the ground is not frictionless. The soccer ball will eventually begin to roll without slipping, which is when the balls center of mass is equal to its angular speed. Now assume that you want to strike the ball so that it immediately begins to roll without slipping. The diagram above shows us how we can accomplish this and the equaltion of s=R(theta) will give us the distance from the center of the ball that you need to kick. The answer to this problem turns out to be s=0.4R, so you would strike the ball a little less than half of the radius above the center line. Friction is a huge factor when considering the game of soccer. When a soccer ball is moving along the field there is constantly a frictional force working in the opposite direction of the balls movement. There is an equation that can be used to find the friction force working against the ball and it is f=mN. This is where f is the frictional force, m is the coefficient of friction, and N is the normal force pointing upward. The coefficient of friction is dependant upon the surface type and ball being used, it is not a constant. This tells us that the coefficient of friction will cause the ball to roll slower when it is large and not as slow when it is small. This also shows that the more friction there is between the ball and the field the slower the ball will roll.
How physics students cheat!
When dealing with projectile motion physics students are normally allowed the assumption of two things;

1) The free-fall acceleration g is constant over the range of motion and is always directed downward.

2) The effect of air resistance is negligible, meaning there is no air resistance on the projectile.

With these assumptions we find that the projectile?s path is always a parabola.

How this cheating pans out!

In theory this works out okay, but in the real world this is obviously not the case. When watching a soccer ball in flight it is easy to tell

that the ball has more than one force working on it besides it?s mass and gravity. In other words, cheaters never prosper when it comes

to reality.

Airflow

In many situations throughout a soccer game it is necessary to make a ball curve around someone and due to airflow against the ball

this is possible to do. To get a ball to curve you must first put it into a rotating motion. To do this you need to initially kick the ball

off-center so that a side spin is created. A low-drag and high-turbulant airflow is then working agains the ball causing the spin. But,

the speed that the ball is kicked at can also directly effect the curve you get from the ball. If the ball is kicked too hard it will enter a

smooth-airflow, or laminar, phase. This can create a large amount of drag and in turn brings in Bernoulli?s principle and a large

sideways force. This force causes the ball to curve in a direction that is hopefully the one you desired.

Bernoulli?s principle shows that the ball in motion will have an effect due to the airspeed above and below it. The balls movement will also be effected because of the spin (rotation) put on it. Bernoulli?s principle shows that there is a lift pushing out to the side because of the rotation due to air pressure giving it a lift.
Roberto Carlos

Roberto Carlos is a very famous soccer player and many of the things that he does with the soccer ball seem physically impossible. If you do not believe me about the incerdible things that Roberto Carlos has done click on the link below and you will be amazed.

The shots he take are so amazing because they wrap around the defenders and then instantly turn into the corner of the goal. This curvature is due to the fact that there is a low-drag, high-turbulant airflow working against the ball pushing it to the side due to the air resistance. To get his desired curve Roberto Carlos had to kick the ball with enough force to give it an initial velocity fast enough to get passed the defenders before the ball slows down and it?s smooth-airflow stage ends. Then he also had to put enough side spin on the ball to give it a rotating motion. Once past the defenders the ball?s smooth-airflow stage ends and the angular velocity put onto the ball comes into play causing the ball to turn directions. Many people can make a soccer ball curve some, but no one can do it as well as Roberto Carlos.

Another aspect in Roberto Carlos?s game that is amazing is the fact that he can kick the ball at such a fast velocity. In fact, he has been known to kick the soccer ball as hard as ninety miles per hour. When kicking this hard it is hard for the goalie to do anything about it. Here is a clip showing how hard he can kick.

The Ball: Adidas is the leading researcher when it comes to the game of soccer. To an amature soccer player all soccer balls being used probably feel about the same when playing, but the professionals can easily tell the difference between a poorly constructed ball and a nice one. In fact, there is a lot of science involved in the creation of a nice ball and, of course, the physics of the game are taken into consideration throughout this creation process. The ball above is their latest creation called the Fevernova ball. It has recieved a lot of hype due to the components it is made out of. These components include Syntactic Foam with gas-filled micro balloons, transparent PU coat, high solid PU, natural latex, 3 ply raschel knitting, and underglass print. The revolutionary component involved in this ball is the new Sytactic foam that causes the ball to rebound quicker, meaning that the ball should not spin or hook unless the player spins or hooks it and that the ball should whistle when kicked at high velocities. This ball was chosen to be used in the 2002 World Cup for the main reason that with the foam the ball will allow faster and harder shots to impress the crowds around the world.

Boots: It is not until recently that the soccer boot or cleat has been researched. In fact, soccer has received much less attention when compared with other sports in the research department. This research that is now being done is to help reduce injuries and enhance performance. In an experiment, five different shoe designs were tested for ball speed, shoe deformation, and tibial shock. The results of this experiment showed the importance of biomechanical analysis for the improvement of soccer cleats. When considering energy return, it can be expected that larger ball speeds would cause more deformation. It was found that there was one shoe model that had the opposite reaction. Due to this finding it is shown that cleat design is a very important aspect of the game and it is important to continue research in this area.

Shin Gaurds: Shin gaurds are very important to the game of soccer because they are the only protection a player has against other people?s legs and the ball. There are many different forms of shin gaurds out there, but the newest shin gaurds out are made of gel to take the impact of objects. Most shin gaurds are made with plastic, but this is not as protective as gel due to the fact that the gel absorbs some of the impact of the collision as the plastic blocks the collision, but doesn?t absorb much of it. The gel absorbs some of the energy being pushed into the player?s leg reducing pain. They are continuing research in this area to make the game safer for players.

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