Abstract: Positioning apparatus comprises: a first surface; a tubular body and a first end surface at a first end of the tubular body and arranged in contact with the first surface; and surface wave generation means arranged to generate a first travelling surface wave on the first end surface, the first travelling surface wave travelling along a first portion of the first end surface in a first direction, and, while the first travelling surface wave is travelling along the first end surface, to generate a second travelling surface wave on the first end surface, the second travelling surface wave travelling along a second portion of the first end surface in a second direction, the second direction being opposite to the first direction. Interaction between the first surface and the first and second travelling surface waves effects relative movement between the first surface and the tubular body.