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I was listening to a record at our university about friction and its rheological definition. For the first moment I thought that its the normal definition

Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other.

However the lecture pointed out that the rheological definition is different from the normal one. The professor who recorded the lecture is out of town now so I can't ask him.

So I just need to know any idea what is meant by the Rheological definition of Friction and what makes it different from the normal one??

Any help is appreciated

docscience
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zozi
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    I have never met the phrase logical definition of friction. Can you clarify what is meant by logical definition. Are you asking about the underying physical processes? If so, it's an adhesive process. – John Rennie Apr 13 '16 at 19:32
  • There are no "logical" definitions in science, there are only empirical ones. Friction is defined empirically in a number of situations and in other situations it doesn't make sense to talk about friction, at all. The more you know about microscopic physics, the less you will use the term, unless you are in mechanical engineering, where it is unavoidable to deal with. I think you should contact the professor and put him on the spot. As you are portraying it, it seems to make no sense, at all. – CuriousOne Apr 13 '16 at 19:34
  • It was mentioned in the lecture that logical is the real definition of friction not just that its the force opposite direction to motion – zozi Apr 13 '16 at 19:38
  • @CuriousOne if we want to get the best definition of friction, what can it be ??? – zozi Apr 13 '16 at 19:39
  • There is no "best" definition of friction. Friction is a complicated phenomenon and it does not have clearly defined boundaries. Everything you have ever heard about it (high school level?) is pretty much oversimplified and borderline wrong. We are mostly including it in that form in the material because it does play a role in everyday life and people need to get a little bit of an idea why they shouldn't be driving fast when it's raining. To be honest with you, I have NEVER heard anything about friction in university level physics. It's complicated and a fringe specialty topic. – CuriousOne Apr 13 '16 at 19:42
  • @CuriousOne I see thanks for your reply. It's actually a remedial undergraduate course :D

    just one more thing, can you just define friction for me in the simplest way possible, thanks for your time

     – zozi Apr 13 '16 at 19:47
  • I suppose if you assume there is another logical definition of friction, then you would have to say the definition you wrote above is illogical. – docscience Apr 13 '16 at 19:52
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    Perhaps you meant to write rheological. That makes a world of more sense. – docscience Apr 13 '16 at 19:55

2 Answers2

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I'll assume you meant to say "Rheological definition of friction". Rheology deals with the friction of fluid layers against one another and with any solid boundaries. The factors of fluid viscosity determine the frictional forces exterted within a fluid and with its boundaries.

A brief overview of the principles, mathematics can be found here

docscience
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Rheology is the science of flow of fluids and deformation.There two aspects of fluid friction:

  1. During flow of fluid - The friction rises due to slippage of one fluid layer over the other, consuming energy due to viscous resistance
  2. When a body is moving in the fluid it acted upon by what is known as drag force, a force that opposes the motion of the body.

The viscosity is $\mathrm{stress/rate\ of\ strain}$ and viscous drag force experienced by a sphere of radius $r$ moving in the fluid of viscosity $\eta$ with velocity $v$ is $F_d = 6\pi r\eta v$.

Nihar Karve
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Dr. B. R. Gupta
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