In this Section we study the motion of projectiles constrained only by gravity. We revise the model, based on NewtonÕs laws, for the motion of an object falling vertically without air resistance and extend this to two dimensions using vector functions to represent position, velocity and acceleration. It is pointed out that an object falling under gravity or thrown vertically upwards before falling back under gravity are simple examples of projectiles. More interesting projectiles involve horizontal as well as vertical motion. The vector nature of the motion is explored. The influences of launch height and launch angle are explored in various contexts. Also we consider the motion of objects constrained to move on inclined planes (e.g. the balls in pinball machines).