Rotation of a sphere and cube full with water

AI Thread Summary
The discussion revolves around the differences in centripetal force experienced by a sphere and a cube filled with water when rotated around a central point. The cube, due to its geometry, does not exert pressure uniformly on all faces, particularly the face closest to the center, leading to a different force calculation compared to the sphere. The calculations presented indicate that the centripetal force for the cube is significantly higher than that for the sphere, raising questions about the accuracy of these results. Participants are seeking clarification on the methodology behind these calculations and why the forces differ despite similar mass and rotational speed. The conversation highlights the complexities of fluid dynamics and geometry in rotational systems.
Gh778
Messages
419
Reaction score
0
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:
Physics news on Phys.org
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 ?
 

Attachments

  • spc.png
    spc.png
    1.7 KB · Views: 547
  • sectc.png
    sectc.png
    1.7 KB · Views: 522
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?
 
The rope is tied into the person (the load of 200 pounds) and the rope goes up from the person to a fixed pulley and back down to his hands. He hauls the rope to suspend himself in the air. What is the mechanical advantage of the system? The person will indeed only have to lift half of his body weight (roughly 100 pounds) because he now lessened the load by that same amount. This APPEARS to be a 2:1 because he can hold himself with half the force, but my question is: is that mechanical...
Hello everyone, Consider the problem in which a car is told to travel at 30 km/h for L kilometers and then at 60 km/h for another L kilometers. Next, you are asked to determine the average speed. My question is: although we know that the average speed in this case is the harmonic mean of the two speeds, is it also possible to state that the average speed over this 2L-kilometer stretch can be obtained as a weighted average of the two speeds? Best regards, DaTario
Some physics textbook writer told me that Newton's first law applies only on bodies that feel no interactions at all. He said that if a body is on rest or moves in constant velocity, there is no external force acting on it. But I have heard another form of the law that says the net force acting on a body must be zero. This means there is interactions involved after all. So which one is correct?
Back
Top