In this clip, the students are gathered around in a whiteboard circle. They’re discussing modeling a set of keys being tossed in the air, using forces. One student explains that when the keys are in the air, there exists two forces on them, the force of gravity, and the force that the hand had imparted on them. There is a disagreement amongst students regarding whether or not the force from the hand still acts on the keys after they’ve left the hand. The professor points out that once the keys leave the hand, the hand is no longer acting on them, and therefore it isn’t exerting a force on it anymore.
This clip takes place in week 9 (Investigating Forces Part 2). This discussion is based off of students’ work on part A of the “Practice with Force Diagrams: 6 Situations” worksheet.