Hydrostatic underwater weighing is based on which principle?

The correct answer, Archimedes' principle, is foundational for understanding hydrostatic underwater weighing. This principle states that an object submerged in a fluid experiences a buoyant force equal to the weight of the fluid it displaces. In the context of hydrostatic weighing, when a person is submerged in water, the volume of water displaced provides a measure of their body's volume. By comparing an individual's weight in air versus their weight when submerged, the density of their body can be calculated. This method is highly effective for assessing body composition since it allows for a precise measurement of body fat and lean mass based on the principle of buoyancy. Understanding this principle is crucial because it is the core concept that enables accurate underwater weighing techniques used in fitness and health assessments.

The other principles mentioned, while important in their own contexts, do not specifically relate to the concept of buoyancy and the measurement of displacement that is essential to hydrostatic weighing.