Virtual work of constraint forces

  • Thread starter tomjones11
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Main Question or Discussion Point

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)
 

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