Neutral Buoyancy
Definition
The condition in which a solid object's density exactly matches the density of the surrounding liquid; the object neither sinks nor rises and remains stationary at a characteristic depth in a gradient column.
- Condition
- Object density equals surrounding liquid density
- Behaviour
- Neither sinks nor rises
- Use
- Density-gradient column methods
- Field
- Forensic density comparison
Common questions
How is neutral buoyancy used to compare forensic samples?+
A density-gradient column is calibrated with beads of known density, and the depth at which an unknown fragment settles gives its density for comparison to reference materials.
Why is temperature control important for this measurement?+
Liquid density changes with temperature, so an uncontrolled temperature shift changes the equilibrium depth and can produce a misleading density reading.
Related terms
- ASTM E2365
- The American Society for Testing and Materials standard for forensic comparison of glass by density; specifies temperature control, calibration, and precision requirements...
- Bromoform-Bromobenzene System
- The reference liquid mixture used in forensic density-gradient columns and sink-float tests; bromoform (2.890 g/cm³) and bromobenzene (1.495 g/cm³) mix in variable...
- Density
- Mass per unit volume (ρ = m/V), expressed in g/cm³ or kg/m³; a physical property used to compare and discriminate glass, mineral,...
- Density-Gradient Column
- Glass column filled with stepwise layers of liquids of decreasing density (commonly bromoform 2.89 g/cm3 and bromobenzene 1.50 g/cm3 mixed in known...
- DFSS
- Directorate of Forensic Science Services, India; issues the Forensic Laboratory Manual that governs glass and soil examination procedures, including the bromoform-based density...
- ENFSI ENG3-2013
- The ENFSI Glass Expert Working Group guideline for glass comparison casework; specifies the examination sequence, within-source variation requirements, statistical comparison framework, and...
- Hydrostatic Weighing
- Density measurement exploiting Archimedes' principle; the apparent weight loss of a solid submerged in a liquid of known density equals the weight...
- Oscillating-U-Tube Densitometer
- An instrument that measures liquid density from the resonant frequency of a liquid-filled U-shaped tube; precision of ±0.0001 g/cm³, widely used for...
- Pycnometry
- Absolute density measurement using a calibrated-volume flask; the density of a solid is calculated from the mass of liquid displaced when the...
- Sink-Float Test
- Qualitative density screening in which a solid fragment is immersed in a liquid of adjustable density until neutral buoyancy is achieved; the...
- Stokes Settling Formula
- The equation v = 2r²g(ρₛ - ρ_f) / 9η relating the settling velocity of a spherical particle to its radius, the density...