Virtual work of constraint forces

[tomjones11]

On a rigid body we usually use the formula δL=F*δP to calculate virtual work. My problem is about the force. This kind of force exists only before the contact. If I imagine a movement δP of the constrained body outside ,in the free space, I will have δL≥0 but as soon as P moves the force F disappears (and δL=0). Removing the contact, even the force should be removed. We can't have movement and force together
I think the problem is related to the model of rigid body. I don't think a rigid body can exert constraint forces without some trick in the model. If it is rigid, it can't be deformed and so it can't return work. In real world constraint force exist only during the deformations of the body, but here?
I don't understand how I should treat the model of the rigid body in this case.
Thanks (and sorry for my english)

 

[LightHero]

The concept of virtual work is based on the idea that the forces applied to a system can be considered to be acting instantaneously at an arbitrarily small displacement δP. The force F is assumed to remain constant over this small displacement and can therefore be used to calculate the work done by the system. In the case of a rigid body, the force F is assumed to act instantaneously due to the constraints imposed by the body itself. Therefore, when considering a displacement δP in the free space outside of the rigid body, there will be no force acting on the system and therefore no work done (δL=0).However, if the rigid body is subjected to external forces, such as those generated by contact with another object, then the force F will not disappear upon moving the body. In this case, the forces must be taken into account when calculating the work done, and the equation δL=F*δP can be used to calculate the work done by the system.