Generalised energy and energy (lagrangian mechanics)

In summary, the conversation discusses the relationships between kinetic energy, generalised energy, and the Lagrangian in the context of Lagrangian mechanics. The first statement states that if kinetic energy is quadratic, then energy equals generalised energy. The second statement clarifies that saying kinetic energy is quadratic is equivalent to saying that none of the position vectors in a system depend explicitly on time. Finally, the third statement explains that a Lagrangian can be independent of time and generalised energy can be conserved even if kinetic energy is not quadratic and energy does not equal generalised energy. The formulas for generalised energy and energy are also provided for further clarification.
  • #1
supaman5
4
0
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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  • #2
Hopefully putting the formulas for generalised energy and energy might help:

L=T-V (kin-pot)

generalised energy: h= [itex]\sum\frac{\partial L}{\partial \dot{q}}[/itex][itex]\dot{q}[/itex]-L where [itex]\dot{q}[/itex] 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.
 

What is generalised energy in Lagrangian mechanics?

Generalised energy is a concept in Lagrangian mechanics that takes into account both the kinetic and potential energy of a system. It is a scalar quantity that represents the total energy of a system and is conserved in a closed system.

How is generalised energy different from traditional energy?

Generalised energy is different from traditional energy in that it takes into account the constraints and degrees of freedom in a system, rather than just the position and velocity of particles. This allows for a more comprehensive understanding of a system's energy.

What is the role of the Lagrangian in determining generalised energy?

The Lagrangian is a mathematical function that describes the dynamics of a system in terms of its generalized coordinates and time. It is used to derive the equations of motion and can be used to determine the generalised energy of a system.

Can generalised energy be negative?

Yes, generalised energy can be negative. In a closed system, the total energy (including both kinetic and potential energy) is conserved, but the individual components of energy can change. This means that the generalised energy can be negative if the potential energy is greater than the kinetic energy in a system.

How is generalised energy used in practical applications?

Generalised energy is used in various fields of physics, such as classical mechanics, quantum mechanics, and thermodynamics. It is often used to analyze complex systems and is a fundamental concept in understanding the behavior of particles and systems in motion.

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