Fluid Flow Table of Contents
Hydraulic and Pneumatic Knowledge
Fluid Power Equipment
Buoyancy Equation and Review
Buoyancy is an upward force exerted by a fluid that opposes the weight of an immersed object. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus a column of fluid, or an object submerged in the fluid, experiences greater pressure at the bottom of the column than at the top.
Buoyancy is defined as the tendency of a
body to float or rise when submerged in a fluid. We all
have had numerous opportunities of observing the buoyant
effects of a liquid. When we go swimming,
our bodies are held up almost entirely by the water. Wood,
ice, and cork float on water.
When we lift a rock from a stream bed, it suddenly seems
heavier on emerging from the water.
Boats rely on this buoyant force to stay afloat. The amount
of this buoyant effect was first
computed and stated by the Greek philosopher Archimedes. When
a body is placed in a fluid,
it is buoyed up by a force equal to the weight of the water
that it displaces.
If a body weighs more than the liquid it
displaces, it sinks but will appear to lose an amount of weight equal to that of the
displaced liquid, as our rock. If the body weighs less than
that of the displaced
liquid, the body will rise to the surface eventually floating
at such a depth that will displace
a volume of liquid whose weight will just equal its own
weight. A floating body displaces
its own weight of the fluid in which it floats.
Assuming Archimedes' principle to be reformulated as follows,
Aapparent Immersed Weight = Weight  Weight of Displaced Fluid
then inserted into the quotient of weights, which has been expanded by the mutual volume
Density/ (Density of Fluid) = Weight / (Weight Apparent Immersed Weight)
yields the formula below. The density of the immersed object relative to the density of the fluid can easily be calculated without measuring any volumes.:
(Density of Object) / (Density of Fluid) = Weight/ ( Weight  Apparent Immersed Weight)
(This formula is used for example in describing the measuring principle of a dasymeter and of hydrostatic weighing .)
