Physics of the Ball www.oceansiderevolution.com/EINSTEIN_4.htm How and where you kick the ball is the most important aspect within the game of socccer.  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. www.oceansiderevolution.com/EINSTEIN_4.htm  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.