Page:Aerial Flight - Volume 1 - Aerodynamics - Frederick Lanchester - 1906.djvu/130

§ 83 cylinder is equal to the energy internal to the cylinder; that is to say:—

The energy in two-dimensional motion about a circular cylinder having a motion of translation through a fluid is equal to the energy of motion in the cylinder itself, for equal densities, or the energy internal and external are as the respective densities of the cylinder and the surrounding fluid.

In a similar manner it can be shown that the energy accompanying an elliptical cylinder in its motion through a fluid is, densities being equal, the same as for a circular cylinder of diameter equal to the major or minor axis, whichever is placed transversely to the line of motion.