buoyant force

Stability of Floating Bodies

Any floating body is subjected by two opposing vertical forces. One is the body's weight W which is downward, and the other is the buoyant force BF which is upward. The weight is acting at the center of gravity G and the buoyant force is acting at the center of buoyancy BO. W and BF are always equal and if these forces are collinear, the body will be in upright position as shown below.
 

005-floating-body-upright-position.gif

 

Problem 01 - Buoyancy

Problem 01
A piece of wood 305 mm (1 ft) square and 3 m (10 ft) long, weighing 6288.46 N/m3 (40 lb/ft3), is submerged vertically in a body of water, its upper end being flush with the water surface. What vertical force is required to hold it in position?
 

02-001-wood-submerged-in-water.gif           02-001-wood-submerged-in-water-english-units.gif

 

Buoyancy

Archimedes Principle

004-archimedes.gif
Archimedes (287-212 B.C.)

Any body immersed in a fluid is subjected to an upward force called buoyant force equal to the weight of the displaced fluid.
 

$BF = \gamma V_D$

Where
$BF$ = buoyant force
$\gamma$ = unit weight of fluid
$V_D$ = volume of fluid displaced by the body
 

 
 
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