ABSTRACT
We are all familiar with Archimedes’ principle, which states that an object immersed in a liquid (e.g., water on Earth) experiences an upward (buoyant) force equal to the weight of the displaced liquid. This millenarian principle is true provided the influence of surface tension, γlv, can be neglected, for example, for sufficiently large objects (think of people and ships). However, small dense objects can float at the water’s surface even when their densities are much larger than the density of liquid water, violating Archimedes’ principle in its initial classical formulation. If we consider small hydrophilic particles, capillarity pulls them deeper into the water, so that the mass of the displaced liquid exceeds the particle mass. In the case of small hydrophobic particles their mass is greater than that of the liquid they displace.
