In this experiment, students analyze the motion of a rubber stopper as it follows the path outlined in the picture below. One end of a string of length l is attached to a horizontal rod at point o. The other end of the string is attached to a rubber stopper of mass m. The string is initially held parallel to the floor and then released. As the string becomes perpendicular to the floor it strikes a second horizontal rod a distance d below the pivot point o, altering its path. The objective is to find the minimum distance d such that the string remains taut as the stopper reaches the points.

When should lab be done?
This lab may be done as a lab practical after all Newtonian kinematics

What should students learn?
Students should learn how to solve a problem using uniform circular motion, forces, and energy conservation.

Teacher Notes:
This is a problem that is more often used in college-level text books.