If one defines the drag coefficient c using

F= 0.5 c rho A v^2

and uses A as the cross section, rho as the density of water, v the speed, and F the drag force,
what is the drag coefficient of a dolphin? (Some use the Surface of the dolphin as A; that gives another coefficient, the surface drag, not the drag coefficient sought here.)

Thank you for any help!

mm


P.S. The answer goes into the new version of my free physics textbook
( http://www.motionmountain.net )

A fun question? ..

I can see three possible (unhelpful) approaches ..

1/ Guess the maximum (horse)power a dolphin can deliver and use the (known?) maximum speed of a dolphin.
2/ When trained to jump vertically it may be that the maximum F they can deliver is limited by ma rather than drag .. from max F and max speed we get drag.
3/ Calculate from energy .. fish eaten, subtract basic metabolism.. estimate time spent cruising at various speeds .. guess efficiency of tail as a motor .. etc.

Some years ago it was suggested that dolphin skin is 'active' in drag reduction .. as far as I know their skin is now regarded as passive .. but 'slippery'.

All very vague.. any better ideas?

-C2.