Apparatus for teaching mechanics including: support means having a plurality of mounting locations in spaced relationship from each other mounting location, a plurality of mechanical elements each mountable to any one of said mounting locations of said support means for rotation about a rotation axis, wherein: the spacing of the mounting locations is such that a pair of mechanical elements mounted one to each of any adjacent pair of mounting locations are in mechanical association with one another for contra-rotation with respect to one another; and further such that when the number of mechanical elements mounted to successive adjacent mounting locations in a closed loop of mechanical elements is not divisible by two, rotation of the mechanical elements is not possible by virtue of the respective mechanical association with one another.