Using history to foster critical scientific thinking: Aristotle and Galileo's debate resolved through high-speed motion tracking in the classroom

In his Discorsi, Galileo aimed to correct centuries of Aristotelian "unreason" concerning the physics of falling objects by introducing a thought experiment that pointed out contradictions when combinations of one light and one heavy body are dropped. Inspired by Galileo's story, we sought to formulate research questions and design experiments for students to enable independent learning based on the history of science. The experiments involve commonly used or inexpensive equipment and free software, and show that Aristotle and Galileo did not disagree about falling objects, but were focusing on different kinds of motion. We assess data generated by high-speed video motion tracking of the fall of various combinations of simple handmade paper cones, following closely the discussion between Simplicio, Salviati and Sagredo in the Discorsi, and demonstrate that every statement in Galileo's reductio ad absurdum holds true and that his argument is in fact free of contradiction. (C) 2018 American Association of Physics Teachers.