In an experimental setup by Henry Kater, the mathematical expression [read slowly] “four pi squared D over T squared” is used as an approximation involving a reversible one of these objects. Dynamic stabilization is typically shown using one of these (15[1])objects named after (15[1])Kapitza. Calculating the Lagrangian of (15[1])one system involving these objects contains the term (*) [read slowly] (10[1])“3 cosine theta-sub-one minus cosine theta-sub-two”; that dynamical system involves two of these objects coupled together. In introductory physics classes, using the small angle approximation reduces the motion of these systems to simple harmonic motion. For 10 points, name these swaying objects that usually consist of a mass attached to the end of a string or a rod. ■END■