Rotation of a sphere and cube full with water

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Discussion Overview

The discussion revolves around the centripetal forces acting on a sphere and a cube, both filled with water, when they are rotated around a central point. Participants explore the differences in pressure exerted by the water in each shape due to their geometrical configurations and the implications for calculating centripetal force. The scope includes theoretical reasoning and mathematical calculations related to rotational dynamics.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant calculates the centripetal force for the cube and sphere, suggesting that the cube experiences a significantly higher force due to its shape and the distribution of water pressure.
  • Another participant questions why the net centripetal force would not be the same for both containers if they have the same mass, distance from the axis, and rotational speed.
  • Further calculations are presented for different shapes, including a triangle, with varying results for centripetal force based on the geometry and water distribution.
  • There is a request for clarification or resources to better understand the calculations and concepts involved.

Areas of Agreement / Disagreement

Participants express differing views on the calculations of centripetal force, with some supporting the initial calculations while others challenge the assumptions made regarding pressure distribution and force application. The discussion remains unresolved regarding the correctness of the calculations and the underlying principles.

Contextual Notes

Participants have not reached consensus on the method for calculating centripetal force in this context, and there are unresolved assumptions regarding the distribution of water pressure in the cube and sphere.

Gh778
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Hi,

A sphere and a cube full at 99.99% with water are put in symetrical position to the center C. Sphere at right and cube at left for example. When they turn together at the center C, the centripetal forces are not the same. The cube has not water all around faces, especially the face closed to the center C and this face can't put pressure (we arrange the shape for that). The sphere can put pressure in the direction of the center even the sphere is at 99.99% with water.

Example:

R=100m
side of cube = 1m
Radius of sphere = 0.62 m
Volume of sphere = volume of cube = 1m
Mass of sphere = mass of cube = 1000 kg
Rotational speed = 10rd/s

For the cube F=1000*100*100.5 = 10.05 e+6 N

For the sphere F=1000*100*(100.3-99.7) = 60000N

Is this result is correct ? Or if not have you the method ?

Edit: we can turn or make oscillation +/- 30 ° around, but this create a force and I think the result is not good but why ?
 
Last edited:
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I added a drawing.

I added result for a cube and a triangle full with water

With:

A rotational speed of w=10rd/s
A radius of R=100m
A cube of 1 m of side full with water, m=1000kg
A isoscele right rectangle of base = 1.5m , h=0.75m, proof = 1.77m => volume =1 m3, m=1000kg (full with water)

The centripetal force for the cube is like m*w²*R = 1000*100*100 = 10e+6 N

The centripetal force for the triangle is like m*w²*100.25-m*w²*99.97*0.28 = 7.2e+6N
0.28 because the weight increase of x² in the triangle
100.25 m and 99.97 m are where the force is apply

Like this the result is right ?
 

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Last edited:
Nobody ? I can't find something with internet. Maybe you have a link to explain this ?
 
I'm not understanding the issue. If the two containers of water have the same mass, distance from the axis, and speed why wouldn't the net centripetal force be the same for both?
 

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