A Demonstration of the Surface Tension of Water

I thought some of my readers might be interested in a demonstration that I worked up to show my thermodynamics students that surface tension can exert a force by which it can do work. The result is certainly not what you expect, and I think it is fairly dramatic.

7 Comments

  1. David H says:

    Yes, I was impressed that the surface tension on the mesh was able to exert a force that strong. But I think you are mistaken in the wording of this post when you said “surface tension can exert a force by which it can do work”. According to my understanding of physics:

    work = force x distance

    It looks like no work was actually done by the surface tension.

    1. Jay Wile says:

      I agree no work is done in that demo. That’s just to show that surface tension can exert a force. Surface tension work is involved when the surface expands or contracts so that the force is exerted over a distance. See page 2, slide 4.

      1. David H says:

        Ah, that makes sense. And actually, when you turned that jar upside-down in the demo, the membrane in each square of the mesh probably bulged out a little, so some small amount of work was involved there.

        In that linked slide there is this line:

        “e.g., for 2D liquid film, infinite work done to create additional surface area dA:”

        Is that word “infinite” correct? Or should it be “incremental” or “infinitesimal”?

        Note to my wife if she sees this post: No I’m not picking on Dr. Wile. This is just how engineers and scientists roll, we review each others’ work. If someone finds something that needs to be fixed, we thank them. If it turns out it wasn’t something that needed to be fixed, the reviewer learns something. It’s all good. 🙂

        1. David H says:

          Oh wait, looking at the link, it is hosted at a Physics department at a university in Canada. That slide wasn’t written by you, you were just supplying a helpful link Never mind the review then.

          (Reviewer learns something …)

        2. Jay Wile says:

          Thanks anyway, David. You are correct. It should be infinitesimal. You are also right that there was a small amount of work, because the mesh does bulge.

  2. John says:

    Wow, great experiment as always!

  3. Lawrence Dol says:

    That’s both cool, and interesting. Thanks Jay.