Surface tension problems and lab work

The idea is simple: touch a wire frame to water and pull it up slowly. Just before the frame leaves the water, the dynamometer shows the frame’s weight F₁ plus the surface tension force, F₂ = F₁ + F. So the surface tension force is F = F₂ – F₁. If l is the length of the line along which water touches the wire (for thin wire, close to twice the frame’s perimeter, counting inner and outer sides), then σ = F/l. Repeat with triangle, square and circle frames, take the mean of the results and compare it with the table value 0.073 N/m for water. The work is done with clean water and a soft dynamometer under the teacher’s supervision; never pull beyond the dynamometer scale.