Recent content by Gh778

  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.
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