Overflatespenninger

Overflatespenninger is the term used in Norwegian (and Danish) for surface tension, the cohesive force at the surface boundary between a liquid and a gas, or at the interface between two immiscible liquids. It is defined as the force per unit length acting along the boundary of the surface and is measured in newtons per meter (N/m). In a liquid exposed to air, it quantifies the energy required to create new surface area and is a central concept in fluid mechanics and thermodynamics.

The phenomenon arises from cohesive forces among liquid molecules and their interactions with the surrounding phase. The classical description is linked to the Young–Laplace equation, which relates the pressure difference across a curved interface to surface tension and curvature. Surface tension influences droplet formation, wetting of surfaces, capillary rise in thin tubes, and the shape of liquid interfaces.

Interfacial tension refers to the same concept at the boundary between two immiscible liquids and can vary with temperature, impurities, and the presence of surfactants. Surfactants are substances that lower surface tension by concentrating at interfaces, enabling processes such as emulsification and foaming. Typical values include about 72.8 mN/m for pure water at 20°C, with many additives reducing the tension further.

Applications of overflatespenninger span detergents, coatings, inkjet printing, emulsions, and microfluidic devices. In biology, surface tension is essential for pulmonary surfactants that reduce alveolar tension in the lungs. Overall, overflatespenninger connects thermodynamics, fluid mechanics, and material science, serving as a fundamental parameter in the study of liquids in contact with gases or other liquids.