What principle does hydrostatic weighing use to estimate body density?

Hydrostatic weighing estimates body density based on Archimedes' principle of buoyancy. This principle states that an object submerged in a fluid experiences an upward buoyant force equal to the weight of the fluid that the object displaces. In the context of hydrostatic weighing, when a person is submerged in water, the volume of water displaced by their body provides a measure of their body volume. By measuring the weight of the person in air and their weight while submerged, the calculation of body density can be made using the difference in buoyancy. This method allows for an accurate estimation of body composition, differentiating between lean body mass and fat mass, which is crucial for fitness and health assessments.

Other principles are not applicable here—Bernoulli's principle relates to the behavior of fluid dynamics in motion, Newton's laws deal with force and motion, and Pascal's principle pertains to pressure changes in fluids. Each of these principles does not directly apply to the measurement of body density through volume displacement as Archimedes' principle does.