Added mass
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Added mass is the inertia added to a system due to the fact that an accelerating or decelerating body must move some volume of surrounding fluid as it moves through it, since the object and fluid cannot occupy the same physical space simoltaneously. For simplicity this can be modelled as some volume of fluid moving with the object. The added mass force opposes forces, and acts similarly to drag, although the two are only superficially similar.
Not to be confused with relativistic mass increase.
[edit] Applications
The added mass can be incorporated into most physics equations by considering an effective mass as the sum of the mass and added mass.
That is, the classical F = m * a becomes F = (m + added mass) * a.
Added mass for a sphere = :<math>\frac{\rho 2 \pi r^3}{3}</math>
r = radius of the sphere
Added mass for a cylinder = Density of liquid * Volume of Cylinder
Added mass for any object = Added mass constant for object * Density of fluid * Volume of displaced fluid
