roll up a tube with pressure inside it. If there is no pressure at external, there is a work give from the tube, because the red trajectory seems to give a work ?
The force F seems to work:
Sure, there is a difference of surface inside/outside circle. But with a big radius for the wheel: 100 m, and a tube of 1cm the difference of surface is only of 6.28 cm and this don't depend of the radius. If I take a radius of 1000 m the difference of surface is always of 6.28 cm. But the works is not the same with a radius of 100 m or 1000 m, no ? The force from F seems to be constant, but the force from surface seems to change with the percentage of roll on wheel, at start to roll up, F seems to give more than difference of surface, at the middle the sum of force seems to be lower. Is it possible to compute the sum of force at each time ?
I think it's logical if I think with the lost of red surface. When the wheel turn and move, it's like a very small rotation about the point "Point of rotation". The red surface want to turn anticlockwise the wheel but if this surface deseappear, it could say the wheel want to turn more clockwise, sure the difference is very small.