# Recent content by Gh778

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. ### 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. ### 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. ### 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. ### 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. ### 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. ### 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. ### 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.