Buoyancy
Buoyancy is the resultant force acting on a submerged body.
Buoyancy is defined as the tendency of a body to float or rise when submerged in a fluid. The resultant force acting on a submerged body by the fluid is called the buoyant force and can be expressed as
F = V γ
= V ρ g (1)
where
F = buoyant force (N)
V = body volume (m ^{ 3 } )
γ = ρ g = specific weight of fluid (N/m ^{ 3 } )
ρ = density of fluid (kg/m ^{ 3 } )
g = acceleration of gravity (= 9.81 m/s^{2})
The buoyant force acts upwards.
Archimedes' principle indicates that
"the upward buoyant force that is exerted on a body fully or partially submerged in a fluid  equals to the weight of the fluid that the body displaces"
 if the body weighs more than the fluid  it sinks
 if the body weighs less than the fluid  it floats
Example  Buoyant Force acting on a Floating Box
A plastic box with length 0.3 m and width 0.4 m is submerged 0.1 m into water. The water density is 1000 kg/m ^{ 3 } .
The buoyant force acting on the box can be calculated with (1)
F = (0.3 m) (0.4 m) (0.1 m) ( 1000 kg/m ^{ 3 } ) ( 9.81 m/s^{2})
= 119 N
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Fluid Mechanics
The study of fluids  liquids and gases. Involving velocity, pressure, density and temperature as functions of space and time.
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