Drag force on a magnet moving near a thin conductor

For a magnet moving with velocity ν over a conducting sheet, a proof of the relationship, drag force=(w/ν) (lift force), based upon Poynting's vector, is given. w is a characteristic velocity determined by the conductance of the sheet. A similar result for a right-angle corner, drag force = (w/ν) (lift force + guidance force), is proved in the high-speed limit by considering Maxwell's stress tensor.