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Neutral buoyancy occurs when an object's average density is equal to the density of the fluid in which it is immersed, resulting in the buoyant force balancing the force of gravity that would otherwise cause the object to sink (if the body's density is greater than the density of the fluid in which it is immersed) or rise (if it is less). An ...
(This formula is used for example in describing the measuring principle of a dasymeter and of hydrostatic weighing.) Example: If you drop wood into water, buoyancy will keep it afloat. Example: A helium balloon in a moving car. When increasing speed or driving in a curve, the air moves in the opposite direction to the car's acceleration.
Reduced-gravity aircraft training avoids neutral-buoyancy training's drag problem (trainees are surrounded by air rather than water), but instead faces a severe time limitation: periods of sustained weightlessness are limited to around 25 seconds, interspersed with periods of acceleration of around 2 g as the aircraft pulls out of its dive and ...
Buoyancy also applies to fluid mixtures, and is the most common driving force of convection currents. In these cases, the mathematical modelling is altered to apply to continua, but the principles remain the same. Examples of buoyancy driven flows include the spontaneous separation of air and water or oil and water.
The principle is used to make small toys often called "water dancers" or "water devils". The principle is the same, but the eyedropper is instead replaced with a decorative object with the same properties which is a tube of near-neutral buoyancy, for example, a blown-glass bubble. If the tail of the glass bubble is given a twist, the flow of ...
An object immersed in a liquid displaces an amount of fluid equal to the object's volume. Thus, buoyancy is expressed through Archimedes' principle, which states that the weight of the object is reduced by its volume multiplied by the density of the fluid. If the weight of the object is less than this displaced quantity, the object floats; if ...
If it is much greater than unity, buoyancy is dominant (in the sense that there is insufficient kinetic energy to homogenize the fluids). If the Richardson number is of order unity, then the flow is likely to be buoyancy-driven: the energy of the flow derives from the potential energy in the system originally.
Strictly, the latter force is "buoyancy". Nevertheless, scuba divers, submariners and others tend to describe the net force (buoyancy - gravity) as "positive buoyancy" if the net force is upwards; "negative buoyancy" if the net force is downwards; and "neutral buoyancy" if the net force is zero. That convention is so widespread among those ...