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When two layers of fluids move over each other, a viscous drag is produced. Could you please elaborate on this?

Qmechanic
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Aayoush Adhikari.
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  • Related https://physics.stackexchange.com/q/41324/226902 , https://physics.stackexchange.com/questions/593727/why-is-viscous-force-directly-proportional-to-velocity-gradient?rq=1 – Quillo Mar 06 '23 at 00:23
  • This question can be answered on several levels, can you please [edit] it to specify what you do not understand or would like to know? – Wrzlprmft Mar 06 '23 at 07:56

1 Answers1

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Most common liquids have a property called viscosity, where the molecules of liquid have weak forces of attraction for one another on short distance scales. If you then try to slide one such molecule past another one, you will find that they would rather remain friendly neighbors and it takes a bit of work to push them past one another.

Now once you slide them past one another and set them in motion, each of them will similarly get friendly with their new neighbors and will set them in motion, and they will get new neighbors, and set them in motion, etc., etc. until the kinetic energy of the original molecule pair has been distributed over a much larger number of molecules and the whole body of affected liquid comes to a stop once again. This is called viscous dissipation.

So if you are pushing a solid body through a viscous liquid, the motion of the body is going to continuously set the liquid molecules in motion. This requires a continuous source of work in that the sliding molecules produce a continuous resisting force on the skin of the moving body. We call that force viscous drag.

niels nielsen
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