The discussion revolves around the formulation of D'Alembert's Principle, particularly why it is expressed in terms of virtual displacements rather than actual displacements. Participants explore the meaning and significance of virtual displacements within the context of mechanics.
Participants express differing levels of understanding regarding the concept of virtual displacements, and while some explanations are provided, there is no consensus on a singular interpretation or significance of the concept.
Some participants note that the concept of virtual displacement is not immediately intuitive and may require further study in appropriate texts or documents to fully grasp its implications.
The concept of virtual displacement is not immediate so you have to study it well in suitable texts/documents.debasish panda said:
- Why is the D'Alembert's Principle
∑i(Fi−miai)⋅δri=0
stated in terms of "virtual" displacements instead of actual displacements?
what does the 'virtual displacement' really means and what is its physical significance??
Because in this way only active forces can be considered. Active forces are those forces which doesn't arise in order to make the particle follow the constraints (these last are constraint forces). In the simple example I made in my previous post, active forces are those which make the particle move along the bar (horizontal forces) while constraint forces are those directed vertically, which prevent the mass point to escape the bar. Usually the constraint is still, or it moves in a specific, given way, so the problem is much simpler to solve if it's focalized in finding how the points move in virtual displacement only. But there are also theoretical reasons to focalize on those displacements only, which will be more clear whe you will study lagrangian mechanics.debasish panda said:
- Why is the D'Alembert's Principle
∑i(Fi−miai)⋅δri=0
stated in terms of "virtual" displacements instead of actual displacements?
Doc Al said:See: Virtual displacem
thnx bro...lightarrow said:Because in this way only active forces can be considered. Active forces are those forces which doesn't arise in order to make the particle follow the constraints (these last are constraint forces). In the simple example I made in my previous post, active forces are those which make the particle move along the bar (horizontal forces) while constraint forces are those directed vertically, which prevent the mass point to escape the bar. Usually the constraint is still, or it moves in a specific, given way, so the problem is much simpler to solve if it's focalized in finding how the points move in virtual displacement only. But there are also theoretical reasons to focalize on those displacements only, which will be more clear whe you will study lagrangian mechanics.
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lightarrow