I work in a processing plant where round steel cutting blades are used, e.g. 1-2 mm thick and 15-30 cm in diameter. During normal plant operations, these blades are mounted on machinery and rotated at circa 1000 RPM -- thus they are perfectly flat whose outer edges are beveled inward.

I've noticed that often multiple blades tend to stick together, especially when they are wet (being washed and rinsed with water). Sometimes a generous force is needed to "pry" apart two (or more) blades stuck together.

My question is: Is this from the Casimir effect, or just surface tension?

  • $\begingroup$ In your research, have you seen an estimate for the magnitude of the Cassimir force? How about for surface tension? Also, I would point out, for the sake of clarity, that the first paragraph of this post is completely irrelevant to the actual question. It would make it easier for would-be answerers to take interest if the post were more concise :-) $\endgroup$ – DanielSank Aug 7 '16 at 2:57
  • $\begingroup$ The plates have to be apart, not stuck together, and the force involved is so small that, and i am sorry to say this, but a well nourished house fly could overcome it. $\endgroup$ – user108787 Aug 7 '16 at 3:16
  • $\begingroup$ The first paragraph was meant to give an accurate physical description of the metal plates I'm inquiring about. But, in retrospect, it does sound a little out-of-place. :-\ $\endgroup$ – pr1268 Aug 7 '16 at 4:33
  • $\begingroup$ Also the fact that you observe the effect to be raised when the plates are wet is a key piece of experimental evidence weighing on the answer. $\endgroup$ – WetSavannaAnimal Aug 7 '16 at 7:31
  • $\begingroup$ Add some soap and see if the force changes. If it does, it's probably not Casimir, that's independent of soap concentration. :-) $\endgroup$ – CuriousOne Aug 7 '16 at 7:53

Surface tension is part of it, but probably it's straight adhesion. Glue. A film of water on (for instance) glass can be wiped off, but usually that just thins the film, the last few microns of water film sticks hard to the surface. If two flats have a thick layer of water between them, it's a lubricant (you get streamline flow in the water), but a thin layer has significant shear strength due to viscosity. A thin layer is an adhesive.

Pulling the plates apart requires both making new surface area of the film (and that's the surface tension part), and making a thicker spacing of the plates (which happens if the water film transports water to the 'thick' region, by flow in the thin layer). That flow in the thin layer is very slow because of the water's viscosity.


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