One particularly famous and very simple model is the equation of a falling body: the distance d an object falls is proportional to the square of the time t. If the time is measured in seconds and the distance in feet, the equation relating these two is
2 d = 16t
This equation is a model of falling objects. It can be used to predict how long it takes a cannonball to fall from the top of a 200 foot tower (3.5 seconds). This might be important if your product is designed to drop cannonballs on moving targets.