A reversible one of these objects uses the mathematical expression [read slowly] “four pi squared D over T squared” as an approximation in an experimental setup proposed by Henry Kater. An application to one of these objects illustrates the Berry phase by getting the Hannay angle through decomposition. Calculating the Lagrangian of one system involving these objects contains the term (*) [read slowly] “3 cosine theta-sub-one minus cosine theta-sub-two”; that dynamical system involves two (10[1])of these objects coupled together. In (10[1])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■