A widely used experiment for studying Newton’s Second Law of Motion makes use of a Half-Atwood machine. In this experiment a cart on a horizontal surface is tied to a mass hanging over a pulley. Upon releasing the hanging mass, the cart begins to accelerate. The magnitude of this acceleration is a quantity of great interest as it relates to the amount of the hanging mass. In this lesson, a Half-Atwood machine is constructed using parts from LEGO®’s Simple & Powered Machines Set. Voyager is mounted to the back of the cart with its IR sensor facing a large piece of white foam board. The pulley holder is mounted to the table.