Arguably, the '1/2' in the drag equation is purely decorative, since drag coefficients are already unitless and could just as easily be half as big. Some derivations give more justification for the extra 1/2 than others, but one textbook just calls it 'a traditional tribute to Euler and Bernoulli.'
Current (water) running through the water (wires) causes it to boil, increasing the pressure (voltage), but resisting (impeding) the flow of hydroelectricity (water currents). This is the basis for Ohm's law.