PHY.7:8 - Common Anti-Patterns and How to Avoid Them

Misstep	Consequence	Repair
Use T-V without recovering the interaction	The magnetic force disappears although kinetic energy is constant.	Supply the coupling from the physical theory and vary the complete Lagrangian.
Differentiate coordinates while omitting their moving reference	The prescribed pivot acceleration is absent from the motion.	Differentiate the complete position map, including its explicit time dependence.
Discard a boundary term before deciding what is fixed	A loaded or free endpoint receives the wrong condition.	Retain the term until the boundary freedom and physical contribution are specified.
Use one constraint rule for every velocity restriction	Different variational constructions are treated as the same physical model.	Recover the constraint’s reaction or admissible-variation premise.
Read stationary as minimum	A saddle history receives an unsupported optimality claim.	Use the first-variation result at its established scope and perform the stronger comparison when needed.
Read a changed canonical expression as changed motion	Gauge-related descriptions appear to disagree physically.	Recover the physical quantities and the endpoint term preserved by the transformation.