Tension between droplets and solids

In PhysicsToday.org we found this paper about the tension of a droplet in a solid surface:

"(...) researchers at Yale University and at consumer products manufacturer Unilever have experimentally and theoretically resolved the out-of-plane contributions. Using a confocal fluorescence microscope, the researchers, led by Yale’sEric Dufresne, laced a 20-micron-thick film of silicone gel with fluorescent beads and measured the deformation due to a water droplet. At equilibrium, a one-micron-high ridge, illustrated in the inset, formed in the gel at the contact line. When the researchers factored the gel’s surface tension and thickness into a linear elastic model, they arrived at a nonsingular theoretical solution for stress that closely fit their experimental data. Their model, however, underestimates the deformations in the solid-liquid contact plane, which they believe are caused by pinning or viscous drag. (E. Jerison et al., Phys. Rev. Lett., in press.)—Jermey N. A. Matthews"

in PhysicsToday

Buoyancy and Density

Density

The density of a material is defined as its mass per unit volume. The symbol of density is ρ (the Greek letter rho). In some countries (for instance, in the United States), density is also defined as its weight per unit volume.

Formula

Mathematically: Density = Mass Divided By Volume

where:

ρ (rho) is the density,

m is the mass,

V is the volume.

Different materials usually have different densities, so density is an important concept regarding buoyancy, metal purity and packaging.

In some cases density is expressed as the dimensionless quantities specific gravity (SG) or relative density (RD), in which case it is expressed in multiples of the density of some other standard material, usually water or air/gas.

font Wikipedia

(more information in Wikipedia link).