A giant sling-shot / catapult is used to shoot projectiles of various composition (regular baseballs, rubber pitching-machine balls, soft foam balls, balloons, etc.)  Students make predictions based on initial data collection and analysis, then determine the accuracy of their guesses.  In addition to the various types of projectiles, two more variables are added:  the placement of the hooks that secures each end of the surgical tubing and the height of the release point are varied.  This alters the angle of projection and impacts the resulting distance that each type of projectile travels.  The observation, collection, graphing and analysis of data helps students get a solid introduction to functions that are non-linear in nature.