two-film-surfaces-double-the-edge-force - Surface Tension and Capillarity Step by Step

A film with two faces doubles the checked edge force. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.

highlighted = computed this step

A film edge can have more than one pulling face

The count is a checked input. It is shown separately before it multiplies the same gamma and line length.

n=2\qquad L=4\ \text{m}

The force changes with the face count

First compare the one-face and two-face domain. Then keep two faces and lengthen the line so every row stays checkable.

\begin{array}{c|c|c|c}n&\gamma&L&F\\1&3\ \text{N/m}&4\ \text{m}&12\ \text{N}\\2&3\ \text{N/m}&4\ \text{m}&24\ \text{N}\\2&3\ \text{N/m}&6\ \text{m}&36\ \text{N}\\\end{array}

Two film faces double the edge force

The doubled force comes from a checked two-surface count, not from a caption-only multiplier.

F=n\gamma L=2\cdot3\ \text{N/m}\cdot4\ \text{m}=24\ \text{N}