When a massless body is being accelerated in an ideal fluid (no viscosity), the necessary force to accelerate the body is proportional to the acceleration in a manner analogous to Newton's law $F = m a$. The coefficient of proportionality is the added-mass or the effective mass os fluid that surrounds the body and must be accelerated with it.

The added-mass can be interpreted as a particular volume of fluid particles that are accelerated with the body. Strictly, however, the particles of fluid adjacent to the body will accelerate to varying degrees, depending on their position relative to the body. In principle, every fluid particle will accelerate to some extent as the body moves, and the added mass is a weighted integration of this entire mass.


Timothy S Choe
2003-03-15