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Number density. The number density (symbol: n or ρN) is an intensive quantity used to describe the degree of concentration of countable objects ( particles, molecules, phonons, cells, galaxies, etc.) in physical space: three-dimensional volumetric number density, two-dimensional areal number density, or one-dimensional linear number density.
Hydrostatic weighing. Hydrostatic weighing, also referred to as underwater weighing, hydrostatic body composition analysis and hydrodensitometry, is a technique for measuring the density of a living person's body. It is a direct application of Archimedes' principle, that an object displaces its own volume of water.
Density ( volumetric mass density or specific mass) is a substance's mass per unit of volume. The symbol most often used for density is ρ (the lower case Greek letter rho ), although the Latin letter D can also be used. Mathematically, density is defined as mass divided by volume: [ 1] where ρ is the density, m is the mass, and V is the volume.
Molar volume. In chemistry and related fields, the molar volume, symbol Vm, [ 1] or of a substance is the ratio of the volume ( V) occupied by a substance to the amount of substance ( n ), usually at a given temperature and pressure. It is also equal to the molar mass ( M) divided by the mass density ( ρ ):
The Sears–Haack body is the shape with the lowest theoretical wave drag in supersonic flow, for a slender solid body or revolution with a given body length and volume. The mathematical derivation assumes small-disturbance (linearized) supersonic flow, which is governed by the Prandtl–Glauert equation. The derivation and shape were published ...
A wide variety of body composition measurement methods exist. The gold standard measurement technique for the 4-compartment model consists of a weight measurement, body density measurement using hydrostatic weighing or air displacement plethysmography, total body water calculation using isotope dilution analysis, and mineral content measurement by dual-energy X-ray absorptiometry (DEXA). [1]
The area density (also known as areal density, surface density, superficial density, areic density, mass thickness, column density, or density thickness) of a two-dimensional object is calculated as the mass per unit area. The SI derived unit is the kilogram per square metre (kg·m −2 ). A related area number density can be defined by ...
Displacement (fluid) Measurement of volume by displacement, (a) before and (b) after an object has been submerged. The amount by which the liquid rises in the cylinder (∆V) is equal to the volume of the object. In fluid mechanics, displacement occurs when an object is largely immersed in a fluid, pushing it out of the way and taking its place.