Generalised energy and energy (lagrangian mechanics)

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SUMMARY

The discussion focuses on the relationship between kinetic energy, generalized energy, and Lagrangian mechanics. It establishes that if kinetic energy is quadratic, then energy equals generalized energy. Additionally, it clarifies that a quadratic kinetic energy implies that position vectors do not explicitly depend on time. Furthermore, it asserts that a Lagrangian can be time-independent, leading to conserved generalized energy, even if kinetic energy is not quadratic, resulting in energy not equating to generalized energy. Key formulas discussed include L = T - V for the Lagrangian and E = T + V for energy.

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  • Understanding of Lagrangian mechanics
  • Familiarity with kinetic and potential energy concepts
  • Knowledge of generalized coordinates and their derivatives
  • Basic grasp of conservation laws in physics
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  • Study the derivation of the Lagrangian and its applications in mechanics
  • Explore the implications of time independence in Lagrangian systems
  • Learn about the conditions under which generalized energy is conserved
  • Investigate non-quadratic kinetic energy systems and their effects on energy conservation
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Students and professionals in physics, particularly those studying classical mechanics, Lagrangian dynamics, and energy conservation principles.

supaman5
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I'm doing lagrangian mechanics and trying to understand my notes, are these three statements correct:

1. If kinetic energy is quadratic then energy equals generalised energy.
2. Saying kinetic energy of a system is quadratic is the same as saying none of the position vectors in a system depend explicitly on time.
3. A lagrangian can be independent of time (generalised energy is conserved) even if kinetic energy is not quadratic (energy DOESN'T equal generalised energy)
 
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Hopefully putting the formulas for generalised energy and energy might help:

L=T-V (kin-pot)

generalised energy: h= \sum\frac{\partial L}{\partial \dot{q}}\dot{q}-L where \dot{q} should be bold and is the time derivative vector for all generalised coordinates.

and energy: E=T+V

Took me about an hour to write out that formula...FAIL.
 

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