Pressure differences create the net force, rather than pressure at a single point. Because pressure increases with depth, the lower portions of a submerged object experience a different pressure environment from the upper portions. Adding the pressure effects over all surfaces leaves a resultant upward force. This is why fluid pressure can support an object even when no mechanical support is present.
Archimedes’ principle converts the pressure result into a usable force balance: the upward force equals the weight of the fluid displaced by the object. Comparing that force with the object’s weight identifies three outcomes: upward motion, downward motion, or neutral buoyancy. The comparison is therefore a static-equilibrium test as well as a way to predict motion.
Depth and fluid density affect the pressure and the weight associated with displaced fluid, while the object’s size determines how much fluid is displaced when it is fully beneath the surface. These variables change the buoyant-force calculation. In experiments, controlling them helps distinguish whether a measured change comes from hydrostatic pressure, density, or object geometry.
Start by identifying the fluid, the object’s submerged volume, and the object’s weight. Determine the weight of the displaced fluid to obtain the upward buoyant force, then compare the two forces. If the forces balance, the object is neutrally buoyant; if they do not, the larger force indicates whether the object rises or sinks.
Fully Submerged conditions are useful for analyzing submarines and aquatic vehicles because designers must relate vehicle weight to the buoyant force generated by displaced fluid. The same force balance helps evaluate whether a vehicle can remain in underwater equilibrium or tends to move upward or downward. It also connects vehicle behavior to fluid equilibrium.
Underwater instruments are exposed to hydrostatic pressure across their surfaces, so their behavior must be considered in the context of depth-dependent pressure. Applying the fully submerged model helps organize measurements of pressure, buoyancy, and equilibrium. In laboratory experiments, the framework also supports tests involving density and displacement, allowing researchers to compare predicted and observed fluid forces.