The science of Flotation

Human beings float by nature if there is oxygen inside the lungs. How an individual floats is determined by the buoyant force from water and the pull of gravity. It varies considerably between swimmers. It requires technique adjustments because it interacts with any movement principle. This article explains floating from a physics point of view.

Basic Physics of Flotation

When an object floats in dense fluid, it is affected by two forces. One is the ever-present force due to gravity and the other is the buoyant force, a force exerted by the fluid on the object. When the object is symmetrical, such as a rectangular block of Styrofoam, the two forces coincide. When the object floats, the buoyant force equals the gravitational force. Since the floating object displaces its weight in fluid (Archimedes’ Principle), equilibrium is reached and the Styrofoam block rests at the surface in the fluid. The water “supports” the weight of the object.

This simple event is illustrated in Figure 1. Confusion often reigns between the roles of the volume and the weight of the water displaced. Archimedes’ Principle is appropriate to understand what occurs. It commonly is stated as follows:

When a body is immersed in a fluid, it experiences an upward buoyant force equal to the weight of the fluid displaced.