We present a simple laboratory activity for introductory-level physics students which involves rolling balls down pipes and analysing their subsequent flight trajectories. Using balls of equal size but different mass allows students to confront their misconceptions of a mass dependence of the exit speed of the balls from the pipes. The concepts of conservation of energy and projectile motion are also utilized as students analyse their data graphically. Adding in concepts of rotational motion improves the predictions. This is a safe and inexpensive laboratory exercise that allows students to clearly see the power of model predictions in understanding the behaviour of physical systems.