Apparent Mass

Apparent Mass


(or associated mass), a quantity having the dimensions of the mass that is added to the mass of a body moving nonuniformly in a fluid medium in order to take into account the action of the medium on the body. For example, if a body with mass m moves with translational motion in an ideal fluid under the influence of the force F, the resistance of the medium is proportional to the acceleration w of the body. In accordance with the fundamental law of dynamics, mw = F – λw or (m + λ)w = F, where the coefficient of proportionality λ is called the apparent mass. Thus, the body moves in the fluid in the same way as it would move in a vacuum if it had the mass m + λ.

The value of the apparent mass depends on the shape of the body, the direction of motion, and the density ρ of the medium. Thus, the apparent mass of a sphere is λ = (2/3)ρπr3, where r is the radius of the sphere. For an elliptic cylinder—that is, a cylinder whose base is an ellipse—moving in a direction perpendicular to one of the axes of the ellipse, λ = ρπa2h, where a is half the length of the axis and h is the altitude of the cylinder.

The determination of apparent mass is of considerable importance in the study of, for example, unsteady motion of bodies fully immersed in water, impact on water, entry of bodies into water, and tossing of ships. In calculations of apparent mass, fluids are assumed to be nonviscous and, usually, of negligible compressibility.


Sedov, L. I. Ploskie zadachi gidrodinamiki i aerodinamiki, 2nd ed. Moscow, 1966.
Lamb, H. Gidrodinamika. Moscow-Leningrad, 1947. (Translated from English.)
Riman, I. S., and Kreps, R. L. Prisoedinennye massy tel razlichnoi formy. Moscow, 1947.


Mentioned in ?
References in periodicals archive ?
On physical examination, the range of motion (ROM) in the neck was almost fully preserved and no apparent mass could be palpated.
The drug K2 was named by authorities this week as the culprit behind an apparent mass overdose in Brooklyn, New York.
On head, chest, and abdominal CT, head and spinal MRI, and PET, no apparent mass lesions other than the thoracic spinal epidural mass were observed (Figure 2).
The source [1] suggested that the emitter's operating area forms a resonant system consisting of the inner elastic cavitation medium, the flow shell properly and the external apparent mass.
1994: The bodies of 48 members of a religious cult are discovered by Swiss police after an apparent mass suicide.
represents the apparent mass transfer coefficient (m [s.
One of the victims of the apparent mass execution seems to be untied and praying in the background, pleading to be spared.
The apparent mass surrender of troops last month came after Kiir repeated an amnesty offer first made to rebel commanders ahead of South Sudan's independence in 2011.
The FLOAT enables transparent support for over-ground gait training in a large 3D workspace, due to its low apparent mass.
But despite the dubiousness of such apparent mass "cyberchondria", the highly respected Pew Research Centre says phone surveys do not support "the oft expressed fear that patients are using the internet to self-diagnose and self-medicate without reference to medical professionals.
I popped into the giant merchandise stall to get over the emotional heartbreak of the apparent mass worm suicide, perusing the paintings section to calm myself down.
Dubai, Jan 15 ( ANI ): An Indian man and his daughter have been found dead inside their apartment in Dubai while his wife is hospitalised in a critical condition in an apparent mass suicide attempt.