Soccer Ball Physics

When a soccer ball is kicked the resulting motion of the ball is determined by Newton's laws of motion. From Newton's first law, we know that the moving ball will stay in motion in a straight line unless acted on by external forces. A force may be thought of as a push or pull in a specific direction; a force is a vector quantity. If the initial velocity and direction are known, and we can determine the magnitude and direction of all the forces on the ball, then we can predict the flight path using Newton's laws.

This slide shows the three forces that act on a soccer ball in flight. The forces are shown in blue and include the weight, drag, and lift or side force. Lift and drag are actually two components of a single aerodynamic force acting

In general, the magnitude of the weight depends on the mass of an object as determined by Newton's law of gravitation. By rule, the weight of a major league soccer ball is one pound. A soccer ball is hollow and inflated with high pressure air, so the weight is distributed around the outside of the ball. But we can often think of the weight as collected and acting through a single point called the center of gravity. The center of gravity is the average location of the weight of an object. To first order, the center of gravity for a soccer ball is located at the exact center of the ball. In flight, the ball rotates about the center of gravity. Newton's laws of motion describe the translation of the center of

Airplane wings generate lift to overcome the weight of the airplane and allow the airplane to fly. A rotating cylinder and a spinning ball also generate aerodynamic lift. Like the drag, the magnitude of the lift depends on several factors related to the conditions of the air and the object, and the velocity between the object and the air. For a spinning ball, the speed of rotation affects the magnitude of the aerodynamic force. The direction of the force is perpendicular to the axis of rotation as noted on the figure.

The orientation of the axis of rotation can be varied depending on how the ball is kicked. If the axis is vertical, the lift force is horizontal and the ball can be made to curve to one side. In soccer this is called "bending" the kick. If the axis is horizontal, the lift force is vertical and the ball can be made to dive or loft depending on the direction of