# Football Physics

## Collisions

Momentum is a vector describing a "quantity of motion". A football player with more momentum is hard to stop, which is desirable. As momentum is the product of mass and velocity, a player can get more momentum by either increasing his mass or by running faster. The training program of many football players is geared towards this.

A running player has kinetic energy, which is equal to ½ mass x velocity squared. Each player in a tackle has their own kinetic energy. It has been calculated that the energy in a collision between two football players could lift 23 tons of concrete an inch into the air. Such energy can cause severe injuries and damage to the body of the football player.

## Throwing a Football

The shape of a football (a "prolate spheroid") gives it unique physical characteristics. Obviously if the ball is thrown sideways it will not go very far, as there will be tremendous drag. However, when thrown with the point of the ball forward it cuts through the air, the drag is reduced, and it travels great distances. In addition, the spin that a quarterback puts on the ball makes it a gyroscope and increases stability. A good quarterback can put a spin of 600 rev/min on the football.