[10] Tractive force: This refers to the force described hydraulically as 'Shear force' — the force that acts to 'shear off' or to dredge and dislodge sediment. In German the term for shear force is 'Schubkraft', meaning 'to push, to shove' as well as 'to shear', whereas Viktor Schauberger uses the word 'Schleppkraft'. The verb 'schleppen' means to drag, draw or pull. Viktor Schauberger's choice of 'Schleppkraft' here is quite specific, since in his view the movement of sediment is due to the sucking action of fast flowing, dense cold water downstream, rather than to the mechanical impact of the water coming from upstream. In view of this subtle change in emphasis, in lieu of the hydraulically correct term 'shear force', the term 'tractive forces' will be used. This dynamic is similar to the effect of wind on roofs, where a roof is blown off not by force from the windward side, but rather by the sucking effect of vortices created on the leeward side. -Ed. [The Energy Evolution - Harnessing Free Energy from Nature, The Biological Vacuum - The Optimal Driving Force for Machines]