Mechanics, as we studied it in the first three chapters, is based on two fundamental principles. On the one hand one makes use of simple functions such as the Lagrangian function and of functionals such as the action integral whose properties are clear and easy to grasp. In general, Lagrangian and Hamiltonian functions do not represent quantities that are directly measurable. However, they allow us to derive the equations of motion in a general and simple way. Also, they exhibit the specific symmetries of a given dynamical system more clearly than the equations of motion themselves, whose form and transformation properties are usually complicated.
KeywordsInertial Frame Lorentz Transformation Rest Mass World Line Inertial System
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