Holonomic constraints and multiplier forces
For ideal independent holonomic constraints f_α(q,t)=0, constrained Lagrange equations can retain redundant coordinates through d(∂L/∂q̇_i)/dt−∂L/∂q_i=Σ_α λ_α∂_i f_α.
Key knowledge
For ideal independent holonomic constraints f_α(q,t)=0, constrained Lagrange equations can retain redundant coordinates through d(∂L/∂q̇_i)/dt−∂L/∂q_i=Σ_α λ_α∂_i f_α. The multiplier terms represent constraint generalized forces, solved together with the constraints.
Values and equations
d(∂L/∂q̇_i)/dt−∂L/∂q_i=Σ_α λ_α∂f_α/∂q_i; f_α(q,t)=0
- L
- Lagrangian J
- q_i
- Generalized coordinates; coordinate-dependent units
- λ_α
- Multiplier; energy per constraint-value unit
- f_α
- Constraint function with specified units
- t
- Time s
- i,α
- Coordinate/constraint indices
Conditions and scope
- Smooth independent constraints, ideal constraint forces doing no virtual work and regular equations; the sign follows the displayed multiplier convention.
- This holonomic variational rule does not cover arbitrary nonholonomic velocity constraints or friction without their additional dynamical formulation.
Sources · 1
References
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Evidence and review
Newtonian Dynamics: Constrained Lagrangian dynamics: Equations 714–728: constrained variations, multiplier equation and constraint-force interpretation; extends one independent constraint to a sum.
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Entry details
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