##  [Archimedes' Principle](/archimedes-principle-0) 

 Definition

A physical principle stating that a body wholly or partially immersed in a fluid at rest experiences an upward buoyant force equal in magnitude to the weight of the fluid displaced by that body.

 

 

 

 

 

 





## Principle

Principle

Buoyancy arises from the hydrostatic pressure gradient in a gravitational field: the net upward force on an immersed object equals the weight of displaced fluid because pressure increases with depth, producing greater upward than downward resultant on the object's surfaces.

 

 

 

 

 





## Demonstration

Demonstration

A solid metal hull floats when its overall weight is less than the weight of water it displaces; measuring displaced fluid volume with a submerged model provides a practical way to determine density and design flotation (e.g., hydrometers and ship displacement calculations).

 

 

 

 

## Misapplication

Misapplication

Applying the principle without correction to accelerating systems (added mass effects), to fluids far from hydrostatic equilibrium, to cases dominated by surface tension at small scales, or ignoring compressibility and stratification when they are important.

 

 

 

 

 





## Consequence

Consequence

Permits quantitative prediction of floatation and buoyant stability, density measurement by displacement, design of floating structures and submersibles, and understanding of fluid–structure interactions in static or slowly varying conditions.

 

 

 

 

## Reversal

Reversal

When the displaced-fluid weight is less than the object's weight, the object sinks; the inverted statement emphasises that buoyancy is a balance between object weight and displaced-fluid weight rather than an inherent upward 'force' independent of fluid mass.

 

 

 

 

 





## Boundary

Boundary

Strictly valid for fluids at rest or in hydrostatic equilibrium and objects whose motion does not significantly disturb the flow; corrections are required for accelerating bodies (added mass), turbulent or strongly unsteady flows, capillary-dominated regimes, and compressible or stratified fluids.

 

 

 

 

 





## Semantic Tension

Semantic Tension

Tension between interpreting buoyancy as a simple displaced-weight equality versus treating it via pressure-integration or virtual-work formulations; also between static buoyancy and dynamic lift/added-mass phenomena in accelerating or oscillating bodies.

 

 

 

 

 





## Synthesis

Synthesis

Archimedes' principle equates buoyant force to the weight of displaced fluid by relating hydrostatic pressure distribution to net upward force: used within its hydrostatic and scale limits, it enables floatation prediction, density measurement and basic fluid–structure design.