Page:Aerial Flight - Volume 1 - Aerodynamics - Frederick Lanchester - 1906.djvu/89

Stokes law is based on a system of motion of the fluid that has been mathematically investigated and the lines of flow plotted from an equation.^[1] It may be remarked that this system of motion can never exist in its entirety, for it involves an infinite

Fig. 30.

quantity of momentum and an infinite quantity of energy^[2]; in other words, the steady state involves a force applied for an infinite time through an infinite distance; it also constitutes a violation of the principle of no momentum of § 5.

If we suppose that the stress, due to the propulsion or to the

1. Stokes' Scientific Papers (t. iii.).
2. "Hydrodynamics," II. Lamb, 1906 ed., p. 553.

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