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 Kicking


 Kicking a ball is the main performance in soccer, and caused by  several scientific theories. 

 Velocity & Acceleration
- Velocity (speed) and acceleration are related to the forces applied on the ball. The speed of a person who runs towards the ball before a kick affects acceleration, because the speed of the person running before the kick will help to kick the ball harder with the higher acceleration. In Newton's second law, force equals the mass times acceleration F=ma. So the higher acceleration will apply more force to the ball. (In the formula, higher 'a' will result a higher 'F').

 Kinetic Energy & the Conservation of Energy
 - Kinetic Energy is the energy acting on a moving object with the following formula: ½mv² . By the conservation of energy, when an object collides with another object, (assuming that no heat energy produced) the total kinetic energy of the both objects has to be the same after and before the collision. So for example, if a person kicks a ball which is at rest on the ground, (ignoring all other conditions except for velocity and mass) a part of the kinetic energy produced on his foot by kicking will be transferred to the ball to maintain the conservation of the energy.

 Air Drag
- Air drag (sometimes called air
dragAir drag (sometimes called air dragresistance) is the friction that applies in the air acting in an opposite direction to the relative motion of an object. So the air drag is one of the reasons that the ball slows down in the air after kicked. Drag Formula: FD = ½ ρu2ACD ( ρ: density, u: velocity, A: area, CD: drag coefficient). This is why the size, shape and density of the ball are very important factors for the players.

 Gravity
- Gravity is the force that pulls things down with
9.81 m/s2  Gravity pulls the ball down while it travels in the air after kicked. That causes the ball to fall to the ground, with the projectile motion along with drag force. 

 Projectile motion                                                                               projectile motion
- Projectile motion is a motion of an object in the air as the picture on the right, caused by gravity and drag force (aka air resistance). When an object is thrown in the air, it falls down to the ground because of the gravity. And the velocity of the object and the drag force (air resistance) changes the travel distance and time. The soccer ball travels in a projectile motion through the air after being kicked. The best example to see this motion would be a free kick and a corner kick.

 Center of the Mass
- Center of the mass is important in order to curve the ball when it is kicked. Center of the mass is where the gravitational force is concentrated. The formula for center of the mass is R = ( ∑m i r i ) / M . Basically, if a person kicks the exact center of a ball, the ball will not spin at all. However, under normal circumstances, a person kicks the ball and it will spin because we can't kick the exact center of the ball due to the unequal surface of the shoes and the ball, and also due to the error of human accuracy.

  Bernoulli's Principal
- Bernoulli's principal states that when speed of fluid or air flow increases, its pressure or potential energy decreases. The following formula explains the reason: Ρ + ½ρυ² + ρgh = constant ( Ρ: pressure, ρ: density, υ: velocity). As you can see in the formula, if the speed (velocity) increases, its pressure or potential energy has to decrease to keep the constant value. This idea helps us to understand the Magnus Effect (that will be explained in the following content).


magnus  Magnus Effect
  - Magnus effect states if an object travels while spinning through the air, there is one side with faster speed and another with slower speed, which will make the object curve. So the side of the ball, where the direction of spin is same as the direction of air flow, has a faster speed than the other side by the Magnus Effect. According to Bernoulli's Principal, since the speed of the spin is faster, the air pressure will be lower. This effect causes the ball to curve.



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  Summary of Bibliography


http://www.slideshare.net/dodrums/the-physics-of-soccer

 The physics of soccer



http://www.bookrags.com/research/kinetic-energy-wop/   Kinetic Energy

http://www.serioussoccer.net/Documents/PhysicsofSoccer.pdf The Physics of Kicking a Soccer Ball

 Science of Soccer author by Wesson, John


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