solid friction

If both cylinders are in a vertical you can't assume a normal force existence, therefore neither a frictional force.

In any other position there will be a weight's component given by Wcos(theta), being theta the angle between the axis and the horizontal.

You means that if both cylindrical pipe are horizontally placed and one is slide inside another pipe,then
we use the formulae
Ff=umg=uR
But by the mordern theory,frictional force arises due to the interaction between molecules on the surfaces when two surfaces
comes in contact, so frictional force also arises even one vertical pipe slide inside the another vertical pipe.But if we observe the same case in point of views of normal force,then frictional force is zero as simply as if both cylinders are in a vertical
we can't assume a normal force
existence, therefore neither a
frictional force.So this may lead the existence of frictional force is about hypothetical in this case.

So, can we use above formulae in case of horizontal pipes?I am just assuming that i am working in the case of horizontal pipe only.

Should we take in account molecular forces in this case? Whether yes, why not in the classical example of a brick sliding on a horizontal surface?

I'm just thinking about classical concepts. Do the molecular forces have such measurable effects?

Should we take in account
molecular forces in this case?
Whether yes, why not in the
classical example of a brick
sliding on a horizontal surface?
Do the molecular
forces have such measurable
effects?

My opinion is that how frictional force is originated is try to be explained by the mordern concept.Mordern concept
can only explain how friction arises betterly than classical concept.Even brick sliding on the horizontal surfaces , frictional force arises by same process.In nature there are different types of force like gravitational force,weak force,nuclear force and electromagnetics force.In this case, we can not apply gravitational force,weak force and nuclear force as they all are small.But we can apply the electromagnetics force as molecules comes together,they can interact properly even they are neutral due to presence of certain electric and magnetic strength of each molecules.
This type of interaction arises in the sliding of brick on the horizontal surface must be intermolecular molecular force.So it must be effective and measurable even in the case of brick and horizontal surface.

Now we combine classical and mordern concept, frictional force arises by mordern concept gives measurement of reaction force by classical concept even in the case of on vertical pipe sliding inside another vertical pipe.Can we do this,yar ?

I believe intermolecular forces should take their place but in an insignificant amount for ordinary macroscopic experiments, the same way that relativistic corrections are not necessary at low velocities. I mean molecular interaction is not actually friction force but a kind of resistance or dissipative force in many cases even less important then the air resistance. Mechanical energy changes should be negligible due to it.

In the most cases, in engeneering, such kind of forces effects must be experimentally measured and not calculated, if they have any practical importance. Any calculus on this must be very difficult.

What's your point of view?

I really mean "should" be very difficult.

Yes, you are also right in your point of view.I am not trying to criticize you but just to explain how frictional force is originated.I think it also be a effect of one of the four forces which are gravitational ,electromagnetic,weak and nuclear forces.So i only guess that it was a effect of electromagnetics force which is regarded as intermolecular force when molecules come together.

lastly i want to ask some question to you.Can I take a permission or not for the materials and datas found in internet for taking them as a reference when during writing a research paper and articles on physics?Further more,
Can you give me some ideas that how can we publish our research articles internationally on the best way.What is the field of your specialization on the science so that if i have any problem related to that field,then your suggestion may be must significant on my future life.If you have no any problems, then you may supply your email id for further direct contact.

Are you believe that when fluid flows,firstly fluid forms layers and then flows like assumed by newton on the viscosity concept.Molecules of fluid have also certain tendency to go randomness even during laminar flow due presence of entropy of fluid.Am i right or not?As Reynolds number increases, fluid flow change from laminar to turbulent but we found that temperature and heat content of the fluid is pratically same.So entropy of the fluid is same even during laminar or turbulent flow.So how turbulence and randomness of the molecules is same originated in fluid in increasing Reynolds number as no significant change in heat content and entropy.This may lead the concept of entropy as hypothetical.

So i assumed that randomness appear on the molecules as on increasing Reynolds number is apperent in nature.If randomness is really originated,then for the validity of entropy concept,heat content of the system ie fluid must be increases which can increase the temperature of fluid by significant amount but it was not significantly observe in nature.So why.Any one have ideas,please you can share?

I realize now you're trying by your own intellectual effort. I imagine that in such common situations as the slid of a brick on a surface, maybe intermolecular forces can't appear, because it exists actually a great distance between them due to irregular surfaces .

About the example of the two cylinders, each must have well-polished surfaces to avoid classical mechanical friction and the idea must be tested experimentally before to try theories that may be destroyed by a single test.

If you have an idea, or an insight, I suggest you to test it before develop a theory. Physics is an experimental science.

I am a simple common person. What I know is what my teachers and books told me. I probably can't help you.