What is surface tension?
Surface tension is the tendency of a liquid's surface to resist external forces, caused by cohesive intermolecular forces between liquid molecules. It acts like a thin elastic membrane on the surface, and is measured as force per unit length (N/m). See also our Friction Loss Calculator.
How do I calculate surface tension on a flat film?
For a flat film, the formula is γ = F / (2L), because a flat film has two surfaces. Divide the applied force (in Newtons) by twice the contact length (in metres) to get surface tension in N/m.
How do I calculate surface tension on a droplet?
A liquid droplet has one surface, so γ = F / L. Simply divide the force acting on the droplet by the contact length. This differs from a bubble, which has an inner and outer surface.
How do I calculate surface tension on a bubble?
A hollow bubble has two surfaces (inner and outer), so the formula is γ = F / (2L) — the same factor-of-two correction as a flat film. Divide the applied force by twice the contact length.
How do I calculate surface tension for a liquid jet?
A liquid jet also has two surfaces, giving γ = F / (2L). The jet can be thought of as a cylindrical film with an inner and outer boundary, requiring the same two-surface correction as a flat film or bubble.
What are the units of surface tension?
Surface tension is expressed in Newtons per metre (N/m) in SI units, or equivalently in millinewtons per metre (mN/m) and dynes per centimetre (dyn/cm). Water at 20 °C has a surface tension of approximately 72.8 mN/m.
How does temperature affect surface tension?
Surface tension generally decreases as temperature increases. Higher temperatures increase molecular kinetic energy, weakening the cohesive intermolecular forces responsible for surface tension. This is why hot water cleans better than cold water.
What is capillary rise and how does surface tension relate to it?
Capillary rise occurs when a liquid climbs up a narrow tube against gravity due to surface tension. The rise height is given by h = (2γ cos θ) / (ρ g r), where θ is the contact angle, ρ is liquid density, g is gravitational acceleration, and r is the tube radius. You might also find our Cavitation Number Calculator useful.