Surface Tension

Molecular Size

Also known as the Ben Franklin pond experiment, after a story in B.F's autobiography.

Olive oil with a known volume is dropped onto water. The water has been dusted with lycopodium powder, which floats on the surface. The oil drop expands, pushing the powder aside to form a clear circle, until the oil forms a monolayer. Measuring the area of the monolayer, dividing the volume of the drop by that area, gives the thickness of the monolayer, which is the height of the oil molecule on water.

From our demonstration movie, we found these values. The size of the patch was 62 cm...

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Capillary Action

What it shows:

capillary actionDue to surface tension effects water rises up a narrow bored tube; the rise in height being inversely proportional to the bore's radius.

How it works:

The setup shows the direct comparison between four...

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Double Bubble

What it shows

When two different size soap bubbles are connected together, the smaller diameter bubble will shrink and collapse to blow up the larger diameter bubble. One can use this to demonstrate Laplace's law or the phenomenon of minimizing the surface area of a soap film.

How it works

Laplace's law tells us that the gauge pressure of a spherical membrane is given by 2γ/r, where γ is the surface tension and r is the radius of the sphere.1 For soap bubbles (which have an inside as well as outside surface), the gauge pressure is twice...

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