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  1. Gh778

    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. Gh778

    B Energy to increase the radius of a circle composed of several disks

    No problem. Have a good day !
  3. Gh778

    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. Gh778

    B Energy to increase the radius of a circle composed of several disks

    I don't understand. What do you mean ?
  5. Gh778

    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. Gh778

    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. Gh778

    B Energy needed to increase a volume

    ok I understood thanks !
  8. Gh778

    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. Gh778

    Calculate the forces and the work

    Homework Statement A wheel moves to the rigth and rotates like a wheel of a bike. There are 2 bodies: - the wheel (red circle) + 2 red walls - the black arm The ground is fixed. The black arm can rotate around the red axis. The red axis is fixed to the wheel. There is no friction. The...
  10. Gh778

    Calculate a torque from a pressure

    I change the expression of the force F3 because I divided by 4 but it's because I knew the result (sum of forces =0). So the integrals are: ##F_3x = \int_{-\pi/2}^{\pi/2} \int_{0}^{0.5} x \frac{\cos(\arctan(\frac{1.5+x\sin(y)}{x\cos(y)}))}{(x\cos(y))^2 + (1.5+x\sin(y))^2} dxdy = 0.0264##...
  11. Gh778

    Calculate a torque from a pressure

    Because if I rotate the device of an angle, for example 0.1 rd, then the sum of the energy is not at 0. I studied some others examples, easier, and I always found the sum of energy at 0. For example, if I take the center of rotation of the black arm in the red dot, then the sum of energy is 0...
  12. Gh778

    Calculate a torque from a pressure

    Maybe you don't understand something in the device. It is not so difficult than that. The balls are small like molecules of water, so I can use the law of pressure with a fluid (no friction). The balls have no mass. Imagine the half disk with water under gravity: I can calculate the forces and...
  13. Gh778

    Calculate a torque from a pressure

    It is a homework, I need to write a program to simulate an object in 2 dimensions with graphical animation, I need to apply in my program integrals (and I can't use library, I need to write all the algorythm). I don't understand why I can't use the integrals, I know the law of attraction, so the...
  14. Gh778

    Calculate a torque from a pressure

    I don't know how to use the method of the gradients of the energy. Like I said I need to use the integrals.
  15. Gh778

    Calculate a torque from a pressure

    I would like to know if my forces F1, F2 and F3 and my torques T1 and T2 are correct because it is the part of the question. And after, I would like to know if my integrals about the work on the black arm is correct because the solution must use the integrals.
  16. Gh778

    Calculate a torque from a pressure

    I would like to find the error in my integrals. I think it is the work to change the length of the black arm but I don't find the good integral. The device is not a single body. There is the red wall, it is free to rotate around the fixed red axis. There is the semicircle, it is free to rotate...
  17. Gh778

    Calculate a torque from a pressure

    The black dot is took by the telescopic black arm. I drawn without the red wall and without the balls: The black dot have a circular trajectory (dotted line), radius = 1.5, center = red axis. But this trajectory is controlled by the black arm. The black arm must turn around the green center...
  18. Gh778

    Calculate a torque from a pressure

    Correct I'm not sure to understand your sentence. The red wall is free to turn around the red axis. But there is a motor that force it to turn clockwise (balls are always at the same position in the half disk). The red axis is fixed to the ground: The telescopic arm (black arm) is free to...
  19. Gh778

    Calculate a torque from a pressure

    The semicircle has the black axis of rotation (the center of the circle) and this axis is take by the black arm. Look at the image, it's possible to see it under the balls. But I redrawn without the balls and without the red wall: I drawn 2 spokes but they are not necessary in the same plan...
  20. Gh778

    Calculate a torque from a pressure

    I forgot something important that I added in the message #3, the red wall is not attached to the half circle. There is a motor on the red axis that force the red wall to rotate clockwise and to follow the half disk. I think like it was a fluid (it's a theoretical problem: the balls are very...
  21. Gh778

    Calculate a torque from a pressure

    The forces F1 and F2 come from the pressure on the walls, respectively the red wall and the half circle. F2 is the force from the half circle. The fluid gives a pressure to the half circle and I represent the sum of all forces from pressure on the center of the circle. For me, like the force of...
  22. Gh778

    Calculate a torque from a pressure

    The forces F1 and F2 come from the pressure on the walls, respectively the red wall and the half circle. F2 is the force from the half circle. The fluid gives a pressure to the half circle and I represent the sum of all forces from pressure on the center of the circle. For me, like the force of...
  23. Gh778

    Calculate a torque from a pressure

    Anybody understand my problem ? The integrals are ok ?
  24. Gh778

    Calculate a torque from a pressure

    It's a theoretical problem, the balls are like molecules of water, very small, no friction. The springs replace the gravity. There are 2 bodies.The red wall is a body, and there is another body: the half circle with its black center. The black arm is fixed on this black center so its length must...
  25. Gh778

    Calculate a torque from a pressure

    Homework Statement Hi :smile: Calculate the forces F1, F2, F3. F1 is the force on the red wall. F2 is the force on the black center and F3 is the force from springs on the red center. Calculate the torques T1 from F1 and T2 from F2 and give the energy from these torques for and angle of 0.2...
  26. Gh778

    Does this device give a magnetic field?

    Ok, and to have the magnetostatic field ?
  27. Gh778

    Does this device give a magnetic field?

    Sorry, but I don't undertand how to use your link to find the magnetostatic field, could you explain please ?
  28. Gh778

    Does this device give a magnetic field?

    It's only for one particle ? And I'm looking for the magnetic field at low frequency not the electromagnetic wave.
  29. Gh778

    Does this device give a magnetic field?

    Hello, It's a theoretical question. I take 2 electrostatic particules fixed in a circle. I turn the circle. Is there a magnetic field ? I suppose the angular velocity very high and I suppose the particules are fixed in the circle. The diameter of the circle is very small. I don't want the...
  30. Gh778

    The position of a point in 2 rotations with 2 axes

    Hello, I simulated it on Ansys Spaceclaim. It's ok, a fixed point on the disk moves up/down like I thought (altitude from the ground). The disk rotates around itself without friction and even at start there is no rotation around itself but the angular velocity is lower than the support. The...
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