visciedad

Visciedad is a nonstandard term used in some contexts to denote viscosity, the internal resistance of a fluid to flow due to internal friction. In standard usage, this property is described as viscosity and is central to rheology and fluid dynamics. Viscosity exists in two related forms: dynamic viscosity (μ) and kinematic viscosity (ν = μ/ρ), where ρ is density.

Dynamic viscosity's SI unit is the pascal-second (Pa·s); the older CGS unit is the poise. 1 Pa·s equals 10 poise, and 1 poise equals 0.1 Pa·s. Kinematic viscosity is measured in square meters per second (m^2/s) and is often expressed in centistokes (cSt), where 1 cSt = 1 × 10^-6 m^2/s.

Viscosity varies with temperature and composition. For example, water at 20 °C has about 1.0 mPa·s, while honey is many orders of magnitude more viscous. Viscosity influences laminar versus turbulent flow, pressure losses in pipes, lubrication film thickness, inkjet printing, and polymer processing. In Newtonian fluids, shear stress is proportional to the rate of deformation (τ = μ du/dy); non-Newtonian fluids exhibit more complex relationships between shear stress and deformation rate.

Measurement methods include rotational viscometers (such as cone-plate and parallel-plate configurations), capillary viscometers (e.g., Ostwald, Ubbelohde), and rheometers for full viscoelastic characterization. The concept of viscosity has a long history, with Poiseuille contributing to measurement techniques; the historical unit poise is named after Jean Poiseuille, while the SI unit is the pascal-second.

See also: viscosity, rheology, Newtonian fluid, non-Newtonian fluid.