## The Falling Body Model

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.