Bearing apparatuses (e.g., thrust bearings and radial bearings) are disclosed. Such bearing apparatuses may comprise a rotor including a rotor surface comprising a first superhard material and a stator surface comprising a second superhard material. In one embodiment, the first superhard material may be structured differently than the second superhard material. In another embodiment, the first superhard material may exhibit an average grain size that is smaller than an average grain size of the second superhard material. Mechanical systems including such a bearing apparatus are disclosed, such as, for example, a motor for use in subterranean drilling. Methods of operating and designing bearing apparatuses are disclosed.