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• Users: Gh778
• In Classical Physics
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1. ### B Energy to increase the radius of a circle composed of several disks

I took time to reply because yesterday I said I found my mistake because the angle is half for the friction so I have well the correct result I think. I don't want to be boring, don't reply if you think the question is nonsense. I reply, only, if I have question. Yes, in 2 dimensions is enough...
2. ### B Energy to increase the radius of a circle composed of several disks

No problem. Have a good day !
3. ### B Energy to increase the radius of a circle composed of several disks

The disks rotates CW around A1 and don't rotate around themselves so I don't understand why the forces are not like I drew. I understood my mistake, the angular rotation of the disks around A1 is not 2r it is r because I need to take the mean. Thanks
4. ### B Energy to increase the radius of a circle composed of several disks

I don't understand. What do you mean ?
5. ### B Energy to increase the radius of a circle composed of several disks

The red forces is the sum of the 2 black arrows (forces of friction) on each disk. There is one segment for each disk (violet color). Each segment is attached on the center of the circle and take a disk. I can increase the length of the segments because the circle increases its radius...
6. ### B Energy to increase the radius of a circle composed of several disks

Hi, I take a big number of disks to composed a circle of a radius of 1 m, the blue curved line is in fact several very small disks: I take a big number of disks to simplify the calculations, and I take the size of the disks very small in comparison of the radius of the circle. The center A1...
7. ### B Energy needed to increase a volume

ok I understood thanks !
8. ### B Energy needed to increase a volume

A recipient (cube) of 1m³ is filled of small spheres, there are for example 1000³ spheres inside the recipient. There are also 1000³ elastics that attract the spheres to the bottom. The elastic are always vertical. One elastic for each sphere. One end of the elastic is fixed on a sphere and the...
9. ### Problem with energy in a cycle

Sorry if I don't use good physics words. Hydraulic cylinders is used only for control the position of 4 walls of R2. They don't give additionnal pressure. Because it's not stable for each wall. Inside R2 there is 1 bar (gas), so the pressure push 4 walls, S1, S2 and 2 vertical walls (side wiew...
10. ### Problem with energy in a cycle

No, I control position of S1 and S2 for have the same volume of R2 when it moves down. It's possible with hydraulic cylinder for example. Not at all, I said Fg1 and Fg2 are forces from gas, not from gravity. Inside R2, there is gas under pressure 1 bar, so there is a force on S1 and on S2. Fg2...
11. ### Choose parameters for a system

Since the time I posted the thread I understood. thanks for your help.
12. ### Problem with energy in a cycle

You right, it's because I would like to verify the conservation of energy with integrales. It's a good exercice because I know the solution to correct myself, but not here I don't find. I'm agree with your method but I would like to find my error. Don't forget R2 has no slopes (slopes of the...
13. ### Problem with energy in a cycle

Hi, I compute sum of energy in a cycle and I don't find 0, could you help me to find the error ? I started an equivalent thread in another physics forum but nobody understand. I hope my english is clear enough for understand the problem. The system is under gravity and everywhere outside...
14. ### Liquid helium and curved piston

Yes, I understand math. But I thought these formulas can be used in every case and this one for example. Like I drawn forces, I find a force greater than with a straight line. Even I take in account angles. The force must be the same, no ?
15. ### Liquid helium and curved piston

Formulas must works in every cases I think. Why I can't draw this image ? Where my forces are wrong ?
16. ### Liquid helium and curved piston

Maybe it's for that I don't find the solution. For you, with a finite size atom, the pressure is increased by upper layer or not ?
17. ### Liquid helium and curved piston

You're right the direction must take in account. You consider the size of atom like 0 in your formula ?
18. ### Liquid helium and curved piston

Yes, it's that. If I study last layer, the pressure is different than the straight surface. Why ? because I think there is not the same number of contact on a straight line compared to a curved line. Take a 1/4 circle of radius 1, with atoms with diameter 0.5. in the straight line the force is 2...
19. ### Liquid helium and curved piston

On my picture, forces are lower on curved piston than it must be. I think the pressure must be the same, but I don't understand where is my error in the picture. Like I drawn, the curved piston receive less force due to the position of atoms (black forces).
20. ### Liquid helium and curved piston

Sure, the pressure must be same everywhere, but I "see" a reduced pressure on curved piston maybe this force is canceled by something I gorgot ?
21. ### Liquid helium and curved piston

It's a theoretical study. Like the image showing, the curved piston move in container and need energy for that. In the same time, another piston move up and recover energy. The pressure inside container is always the same (need to control speed of pistons, but there is a pressure). No gravity...
22. ### Choose parameters for a system

Theoretical study. Disks are one above the other. Turn at same rotationnal speed w. Is it possible to choose good parameters for: - density - radius - rotationnal speed - position of d3/gas: d3 in disk1 at radius R1, d3 in disk2 at radius R2, gas in disk1 at radius R2, gas in disk2 at...
23. ### Sum of forces, vacuum and gravity

So, if you're right: imagine a fluid disk (or a sphere) without black solid. I put vacuum object in water, this don't change the CG. After, I let the bubble move, this move water in one direction and vacuum object in other direction, but the vacuum object has no weight, this move the CG ?
24. ### Sum of forces, vacuum and gravity

yes, the force of buoyancy
25. ### Sum of forces, vacuum and gravity

It's a theoretical study. I would like to understand how the sum of forces can be at 0 if I put an object (vacuum in it) in a big liquid disk (disk is fulled with liquid), the disk is big enough for agglomerate liquid (like this works with a planet, matter is agglomarate with gravity). There is...
26. ### Sum of forces

I understood my error, due to the circular shape of balls: balls want to move up and the cone want to move down. Sum of force is zero. But, in this case if density of cone is the same density than balls, this system don't respect Archimède's principle ? The shape change the Archimède's principle ?
27. ### Sum of forces

While awaiting the good model for Comsol, I'm thinking with a static problem that it's easier to find my error. Put a cone in a container with a lot of compressible balls. Gravity is like drawing. Choose diameter of balls for have an integer nomber of balls in each layer, like that it's more...
28. ### Sum of forces

Yes, this is the situation, but balls are not necessary in contact with cone and with others balls if repulsive force is big compared to the "pressure". I'm trying to simulate with Comsol and say how are balls in 3D.
29. ### Sum of forces

The last view is a cutting view (a slice of cone). The cone in the center must receive force from balls. Imagine balls which repuls themselves and cone repuls balls. For receive the pressure balls will be like the last view, but like the shape of balls is a circle all the pressure can be apply ...
30. ### Sum of forces

Sure, it's not moving alone in water :approve: I'm ok with the difference of surface too. I show balls like a circular dam that prevent force to apply on cone's surface, like a protective shield (drawing). When cone is moving, balls move closer from each other for "build" a "circle" (following...
31. ### Sum of forces

I'm drawing a cone (black color) inside balls. Balls are pressured from external force, but the pressure is fixed. Balls repuls themselves and cone repuls balls too. The cut view of cone (bot) showing part of balls all around cone, arrows are forces all around balls. For me F1>F2, because like...
32. ### Efficiency to move a curve shape

ok, so it's Fsb or Fb3 that must be lower/greater, but why, can you explain ?
33. ### Efficiency to move a curve shape

"not equal", the sum is not zero ?
34. ### Efficiency to move a curve shape

For simplify the study, I imagine the black last shape but gravity is not down, it is through the screen and I have only one layer of balls. This is the weight of ball that give pressure (ball can be deformable). I hope the FBD is good ? For me, each force has the same value and depend of...
35. ### Efficiency to move a curve shape

Can I consider balls small enough for use the law of pressure in liquid ? F1 = (h2-h1)*g*σ F2 = h1*g*σ F3x = (h2-h1)*g*σ with σ the density of balls, I consider only F3x because F3y can be cancel by a mechanical system and in this case F2 don't help/prevent the movement (this for reduce...
36. ### Efficiency to move a curve shape

It's a little too difficult for me. I'm thinking an easier shape for understand where is my error. Imagine the black shape in water (new drawing), like that F1+F2+F3 = 0 (vectors), I'm ok with that. But with small balls (not molecules of water), I "see" for each ball in contact with the curve...
37. ### Efficiency to move a curve shape

Don't worry, I'm interresting about efficiency not perpetual motion. If I prevent the blue volume to change and move from pos1 to pos2, in this case, my black forces are wrong, could you explain at least this point ?
38. ### Efficiency to move a curve shape

Fig 1 : the blue volume has a lot of very small spherical balls in it. Balls are under pressure from external system (weight or other), the potential energy is always the same because the blue volume is constant. When I move the blue volume from position 1 to position 2, I can understand that...
39. ### Bolt and nut

The slope is different that's why the nut don't turn with torque I think.
40. ### Bolt and nut

Yes, sorry I change and I don't explain all I think :( I thought with square thread, you're remind ? It's not like the drawing show; With square thread we have calculate the torque increase with the radius not like a circular thread where the torque is the same with different radius. Imagine the...
41. ### Bolt and nut

With a standard bolt and nut. Create 2 areas, red and green, red surface = green surface. Green surface is closer to the center than red surface. Red surface is between up surface of bolt and bot surface of nut. Green surface is between down surface of bolt and top surface of nut. We put the...
42. ### Force on surface with quantification

with mechanicals balls the black volume is blocking, it can't move even a force exist. With gas and temperature, the volume can move (can, I don't say it move). Is a force exist when the slope can accept 5 atoms and other side 1.5 atoms ? I would like to calculate this force but maybe someone...
43. ### Force on surface with quantification

Change red balls for atoms (atoms of gas for example). Even a surface like I draw it's not possible to build. The temperature move atoms everywhere and like that the black volume can move (it's not block by mechanic balls). The vertical line can only put 1.5 contact (even it's statistical), this...
44. ### Force on surface with quantification

I would like to know if there is a force. Like that, even frictionless, no
45. ### Force on surface with quantification

I would like to calculate the force on the black surface (cut view) where the black volume (undeformable) is put on pressure with a lot of red ball undeformable. The pressure is give for example with a weight. Like in the slope we can put 5 balls and only 1.5 balls in vertical side I think the...