Nanomechanical, nanoelectromechanical, and other molecular-scale pump assemblies are described. In certain embodiments, the pump assembly includes a cavity. The cavity includes a plurality of nanofilaments, a surface proximate at least one of the nanofilaments, a fluid flow path, and an opening. Molecules of a fluid that flows from the opening through the cavity along the fluid flow path collide with the surface or one or more of the nanofilaments such that the molecules are accelerated along the fluid flow path. A molecular-scale pump assembly includes a plate defining a plurality of openings, and a plurality of cantilevered molecular-scale beams positioned over each opening. In certain embodiments, molecules of a fluid are accelerated through the opening by asymmetric oscillation and in other embodiments charges are guided along a conductive channel by asymmetric collisions.