Work out surface tension instantly with clear inputs, formula shown and shareable results.
Surface tension is force per unit length along a liquid surface. A wire frame pulled from a film has liquid on both sides, so the measured force is divided by twice the wire length. 14.6 mN on a 10 cm wire with two surfaces gives 0.073 N/m, the accepted value for water at 20 C. The same number is the surface energy in joules per square metre.
Surface tension
gamma = F / (number of surfaces x L)
Bubble pressure
dP = 4 gamma / r for a soap bubble
A film has two liquid-air interfaces, one on each side, and both pull on the wire. A single interface, as in a Wilhelmy plate in bulk liquid, uses one.
About 72.8 mN/m at 20 C - unusually high because of hydrogen bonding, which is why insects can stand on it.