This isn't actually a homework question, but it does relate to a research project I'm doing relating to wind/ocean turbines. What I'd like to be able to do is state that: There is as much energy in an ocean current moving at "X" knots as there is in an air current moving at "Y" kph. I tried using P=1/2(ryo)(v^3)(pi)(r^2), where P is the power produced by the turbine, ryo is the density, v is the velocity, and r is the radius of the turbine. Assuming P is equal in either case, I set the equations (one of water, one for air) equal to each other. I also assumed r was equal in either case, so r, pi, and 1/2 cancel, leaving: (ryo_water)(v_water^3)=(ryo_air)(v_air^3) Using: ryo_air = 1.275kg/m^3 ryo_water = 1025kg/m^3 (seawater) I end up with v_water = 0.1075(v_air) So if I have my conversions right an 8 knot current would have as much energy as a 137.8kph wind. This seems reasonable to me, but it is very low compared to data I can find on the net. Do anyone have any insight on this? Thanks in advance!