Moving Constraints: Virtual Work in Classical Mechanics

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SUMMARY

The discussion centers on the concept of virtual work in classical mechanics, specifically addressing the treatment of moving constraints as outlined by R. Douglas Gregory in his work on Lagrange's equations. It is established that the virtual work done by constraint forces is zero, even in time-dependent scenarios, due to the consideration of the partial derivative of the position vector \( r_i \) with respect to the generalized coordinate \( q_j \). The time derivative is not included in the dot product with virtual velocity, which is a critical aspect of understanding this phenomenon.

PREREQUISITES
  • Understanding of Lagrange's equations in classical mechanics
  • Familiarity with the concept of virtual work
  • Knowledge of generalized coordinates and their derivatives
  • Basic grasp of vector calculus and dot products
NEXT STEPS
  • Study R. Douglas Gregory's "Classical Mechanics" for in-depth understanding of moving constraints
  • Explore the implications of virtual work in non-conservative systems
  • Learn about the role of generalized coordinates in Lagrangian mechanics
  • Investigate advanced topics in vector calculus relevant to mechanics
USEFUL FOR

This discussion is beneficial for students and professionals in physics, particularly those studying classical mechanics, as well as educators seeking to clarify the principles of virtual work and moving constraints.

Sumit Dey
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the virtual work done in the case of moving constraints is obviously not zero(argument as shown in classical mechanics by r douglas gregory page 345 under the heading of Lagrange's equations with moving constraints.i just wanted to understand how come the virtual work done the constraint forces in still zero even in the time dependent cases. why is he just taking into consideration of the partial derivative of the position vector r_i wrt to the generalized coord q_ j only and not the time derivative while taking the dot product with the virtual velocity.. please help!
 
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