He provided the first extensive study of the ways in which a thin film of liquid flows down inclined surfaces.
[2] Liquid film behavior represents a subset of the more general class of free boundary problems.
After World War II Kapitza was removed from all his positions, including director of his Institute for Physical Problems, for refusing to work on nuclear weapons.
[3] Unlike most dimensionless numbers used in the study of fluid mechanics, the Kapitza number represents a material property, as it is formed by combining powers of the surface tension, density, gravitational acceleration and kinematic viscosity.
[4] where σ is the surface tension (SI units: N/m), g is gravitational acceleration (m/s2), ρ is density (kg/m3), β is inclination angle (rad), and ν is kinematic viscosity (m2/s).