This paper is a summary of the results of investigations of the drop in potential and boundary resistance in unsteady motion for cases of surface resistance caused by boundary shear stresses and cases of form-type resistance associated with the high shear and generation and diffusion of turbulence accompanying jet formation. These cases were obtained using uniform diameter conduits and orifices in conduits. From tests in the MIT unsteady flow water tunnel, the effects of accelerated and decelerated flows were studied. In the case of flow through a uniform tube, it was found that the boundary resistance at any instant during accelerated motion was slightly greater than the equivalent steady-state case while, for decelerated motion, it was slightly less. In the case of flow through orifices, it was found that the combined resistance of the orifice and the conduit was less during accelerated motion and more during decelerated motion than for the equivalent steady-state cases.

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