Centrifugal forces + pressure and CG

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Discussion Overview

The discussion revolves around the dynamics of a rotating half torus composed of solid and liquid materials, focusing on the forces exerted by these materials during rotation. Participants explore concepts related to pressure, center of gravity (CG), and the behavior of solids and liquids under rotational motion. The scope includes theoretical considerations and modeling challenges in fluid and solid mechanics.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants question whether water exerts pressure and if solid materials contribute to pressure in the same way as liquids.
  • There is a discussion about the role of a container in holding the liquid and how it applies forces to the liquid, which may affect the overall analysis.
  • One participant suggests that if the solid is imagined as being made of small parts connected by ropes, the pressure could be significantly reduced.
  • Another participant emphasizes the complexity of the problem, noting that both solid and liquid will experience non-homogeneous deformations and that the liquid will exhibit viscous flow.
  • There are considerations about whether the forces from the liquid and solid can be treated as negligible under certain conditions, such as when the angular velocity is constant.
  • Participants discuss the implications of changing angular velocity and how it complicates the analysis of forces within the system.
  • One participant proposes starting with simpler problems to build understanding before tackling the more complex torus scenario.
  • There is a mention of boundary conditions being crucial for determining stress distributions in the rotating system.
  • A question is raised about the applicability of these forces to the Earth's core, indicating an interest in broader implications of the discussion.

Areas of Agreement / Disagreement

Participants express differing views on the nature of forces exerted by solids and liquids, the role of pressure, and the effects of rotational dynamics. There is no consensus on the specific mechanics involved, and the discussion remains unresolved with multiple competing perspectives.

Contextual Notes

Participants highlight the importance of boundary conditions and the complexities introduced by varying angular velocities. The discussion includes assumptions about the behavior of materials under rotation, which may not be universally agreed upon.

Who May Find This Useful

This discussion may be of interest to those studying fluid mechanics, solid mechanics, or rotational dynamics, as well as individuals exploring theoretical models in physics and engineering.

  • #31
Like density of liquid and solid are the same, I think centrepetal forces are the same for liquid and solid, so all centripetal forces cancel themselves and I don't show them on drawings.

Now, forces that I drawn on my last drawings are only forces from pressure of liquid, C and F forces like we spoke before. Like W is constant I don't see others forces. In my second drawing if I put forces for cancel all torques, the support of the system must see a force to the left and up. I think it's logical to say sum of torques is zero. For me, the square part of solid adding reduce C forces at external circle.

It's a difficult problem but interresting too, if someone can help me to pose equations I can be resolve it. The difficulty for me it's to understand what's happen in reality.
 
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  • #32
If you are using centripetal analysis you must use accelerations and Newtons laws.

If you want to do force analysis you must use D'Alembert's method.

I have noted this before.

I have also noted that I do not understand your diagrams or yours arrows in particular.
 
  • #33
I drawn with more details on forces like I think there are. I think it's not necessary to use Newton or Alembert method because my error is enormous when I see sum of forces. I think I forget something in the system.
In the drawing, red forces are forces from centripetal effect, like solid and liquid have same density, sum of these forces are zero.
Green forces are only pressure of liquid but without the centripetal forces (red color for that). We have F and C forces like we see before. For me torques from Fa, Fb and Fc must be to 0 because this system can't give energy from nothing. So I need anothers forces for compensate sum of Fa+Fb+Fc (in vector) but sum of c1+c2+c3+c4+c5 don't do that, these forces are at left too. For me c4 and c5 are lower because there is less water in a radius length due to the presence of solid, solid which give only centripetal forces not pressure. What another forces are in the system ?
 

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  • #34
So with the shape in the drawing, in a small part of rotation F1>F2, this give a torque ? F2 move more than F1 so how torque can cancel ?
 

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