Calculate friction in an unusual manner.

[Thijske]

This is quite a specific case:
I would like to calculate how much friction force is exerted between the rotating rod and the stationary circular thing. I guess we can't just use the formula of static/kinetic friction, because I don't think a normal force is of application... In the image, Fres> is made up of Frod> and Ffriction<. Only Frod is a known force. Also, the coefficients are known. By the way, Frod is the force someone exerts on the rod.

Illustration: https://cdn1.imggmi.com/uploads/2019/12/19/67d76d5ccc990bed5ac4be6922a03021-full.png

 

[BvU]

Hello Thijske, !

I would like to calculate

Sure, but for that you need some input, which is deerly lacking in your story. You draw a star(*) at the point where it hurts most, but the turning point is also a big unknown contributor: if the fit between axis of rotation and cylindrical wall is tight, properties like flexibility of the turning pole come in too. The international standards organisation has a whole book on sets of fits and limits (also https://mdmetric.com/METRIC%20STANDARDS%20for%20Worldwide%20Manufacturing%20summaries.pdf)

Seems to me this has to be determined experimentally.

What does this contraption represent ? Does gravity play a role (you don't say it is a top or a side view)

(*) why not have a wheel or a ball bearing there ?

 

[Thijske]

Hello Thijske, !

Sure, but for that you need some input, which is deerly lacking in your story. You draw a star(*) at the point where it hurts most, but the turning point is also a big unknown contributor: if the fit between axis of rotation and cylindrical wall is tight, properties like flexibility of the turning pole come in too. The international standards organisation has a whole book on sets of fits and limits (also https://mdmetric.com/METRIC%20STANDARDS%20for%20Worldwide%20Manufacturing%20summaries.pdf)

Seems to me this has to be determined experimentally.

What does this contraption represent ? Does gravity play a role (you don't say it is a top or a side view)

(*) why not have a wheel or a ball bearing there ?

Hi, thanks for your response!
In answer to your concerns:
- This drawing is a top view, so gravity doesn't play a role.
- The two components are both made of thick aluminum (flexibility is therefore probably insignificant).
- The turning rod and the circular thing are airtight. Therefore, a bearing of any kind is unfit for the job.
- The turning point is in de center of the entire circle; the turning point has a constant distance to the circle.
- I would rather not do this expirementally, because to construct the entire contraption (including other stuff, that is) would be too expensive.

 

[BvU]

This drawing is a top view

Makes me curious to see the whole thing: side view, height, top/bottom construction, etc.

The turning rod and the circular thing are airtight

Like a revolving door in a store, or like an airlock in the ISS ? How about under and above the rod (apparently not a beam, but a rod?) ? What pushes the turning rod against the circular thing ?

I would rather not do this expirementally

Make a small scale model with the essentials. You'll find that beats any and all calculations.

What does this contraption represent ?

Here you see an interesting phenomenon in research: ask one question, get back five

 

[Dale]

Only Frod is a known force.

Is $F_{rod}$ the force for an angular acceleration or is it moving at a constant angular velocity?

 

[Thijske]

Here you see an interesting phenomenon in research: ask one question, get back five

Yeah I've experienced that a lot lately, so it kind of made me laugh. Anyway, I want to thank you for your time again!

However I'd like you to consider the following: https://cdn1.imggmi.com/uploads/2019/12/20/5f2ca236e50492ac9894f0f286e6276c-full.png

In here, Fpressure is what I meant earlier with Frod. The pressure comes from a comprised gas (red stuff). The gas is pure oxygen (O2). The pressure is known. For the rest, I guess everything from earlier applies to this scenario. I understand that the pressure goes down as the beam/rod/pole/whatever goes to the left, but that doesn't matter, I want to calculate Fn in the most comprised scenario.
My thinking here is that Fn needs to be big enough to keep the oxygen from getting out.
Friction is calculated with Fn.
The question: how do I calculate Fn?

Make a small scale model with the essentials. You'll find that beats any and all calculations.

I would, but this isn't the only friction in the entire contraption. To know all frictions, I'd have to make the entire thing, and that would be a huge project...

Is $F_{rod}$ the force for an angular acceleration or is it moving at a constant angular velocity?

I guess it's the first of the two mentioned options, but I'm not too sure about what you're saying, sorry...