Students study the Atwood machine to verify Newton’s Second Law of Motion. In this machine, two hanging masses are tied to the end of a string that loops around a pulley. The larger mass then moves downward with a constant acceleration, while the smaller mass accelerates upward. The magnitude of this acceleration is a quantity of great interest as it relates to the values of the two masses. In this lesson, an Atwood machine is constructed using parts from LEGO®’s Simple & Powered Machines Set. Voyager is mounted to the bottom of the larger mass with its IR sensor facing a large piece of white foam board on the floor. The range finder data is collected to show that the acceleration is proportional to the mass difference.