dorsal/arxiv
View SchemaVirtual Displacement in Lagrangian Dynamics
| Authors | Subhankar Ray, J. Shamanna |
|---|---|
| Categories | |
| ArXiv ID | physics/0410123 |
| URL | https://arxiv.org/abs/physics/0410123 |
Abstract
The confusion and ambiguity encountered by students, in understanding virtual displacement and virtual work, is addressed in this article. A definition of virtual displacement is presented that allows one to express them explicitly for both time independent and time dependent constraints. It is observed that for time independent constraints the virtual displacements are the displacements allowed by the constraints. However this is not so for a general time dependent case. For simple physical systems, it is shown that, the work done on virtual displacements by the constraint forces is zero in both the situations. For allowed displacements however, this is not always true. It is also demonstrated that when constraint forces do zero work on virtual displacement, as defined here, we have a solvable mechanical problem. We identify this special class of constraints, physically realized and solvable, as the ideal constraints. The concept of virtual displacement and the principle of zero virtual work by constraint forces are central to both Lagrange's method of undetermined multipliers, and Lagrange's equations in generalized coordinates.
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"abstract": "The confusion and ambiguity encountered by students, in understanding virtual\ndisplacement and virtual work, is addressed in this article. A definition of\nvirtual displacement is presented that allows one to express them explicitly\nfor both time independent and time dependent constraints. It is observed that\nfor time independent constraints the virtual displacements are the\ndisplacements allowed by the constraints. However this is not so for a general\ntime dependent case. For simple physical systems, it is shown that, the work\ndone on virtual displacements by the constraint forces is zero in both the\nsituations. For allowed displacements however, this is not always true. It is\nalso demonstrated that when constraint forces do zero work on virtual\ndisplacement, as defined here, we have a solvable mechanical problem. We\nidentify this special class of constraints, physically realized and solvable,\nas the ideal constraints. The concept of virtual displacement and the principle\nof zero virtual work by constraint forces are central to both Lagrange\u0027s method\nof undetermined multipliers, and Lagrange\u0027s equations in generalized\ncoordinates.",
"arxiv_id": "physics/0410123",
"authors": [
"Subhankar Ray",
"J. Shamanna"
],
"categories": [
"physics.ed-ph",
"physics.class-ph"
],
"title": "Virtual Displacement in Lagrangian Dynamics",
"url": "https://arxiv.org/abs/physics/0410123"
},
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