How Does Increasing C Affect Trajectories in Lagrangian Mechanics?

In summary, the problem at hand is to show the existence of a limiting trajectory \vec{q}_{lim}(t) that converges point wise in time, where \vec{q}_C(t) is obtained from a new Lagrangian L_C(\vec{q}) with C>0. This new Lagrangian includes a summation of squared coordinates, representing a force that acts on directions normal to the submanifold M. As C increases, these forces become stronger and potentially force the particle to stay within M. The question remains if this problem has a positive solution or if there are any counter examples.
  • #1
rayohauno
21
0
the problem formulation is the next:

there is a manifold [tex]N[/tex] of dimension [tex]n[/tex]. inside [tex]N[/tex] there is another submanifold [tex]M[/tex] of dimension [tex]m\leq n[/tex].

let [tex]\{q_i\}[/tex] be a coordinate system over [tex]N[/tex] such that [tex]q_i = 0[/tex] for
[tex]i = m+1,...,n[/tex] if the point given by [tex]\vec{q}[/tex] is in [tex]M[/tex].

let [tex]L(\vec{q})[/tex] be a lagrangian over [tex]N[/tex].

and let:

[tex]
L_C(\vec{q}) = L(\vec{q}) + C\sum_{i=m+1}^n (q_i)^2
[/tex]

another new lagrangian over [tex]N[/tex] where [tex]C>0[/tex].

then the problem is to show that there exist a limiting trayectory:

[tex]
\vec{q}_{lim}(t) = lim_{C \rightarrow \infty} \,\, \vec{q}_C(t)
[/tex]

that converges point wise in time. where [tex]\vec{q}_C(t)[/tex] its the trayectory obtained from
[tex]L_C(\vec{q})[/tex] for some (any) initial conditions over [tex]M[/tex].
 
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  • #2
I just want to mention that u may think of the constraints:

[tex]C\sum_{i=m+1} (q_i)^2[/tex]

as if at any point in [tex]N[/tex] there exist some kind of springs that tend to move the particle point to
a some position in [tex]M[/tex].

by definition of the properties of the coordinate system chosen, at each point in [tex]N[/tex] the springs
forces acts on directions normal to the manifold [tex]M[/tex] (if the particle point its close enough to [tex]M[/tex]).

so, enlarging [tex]C[/tex] just makes those springs more stronger, (hope) forcing to the particle live in [tex]M[/tex] in the limiting case [tex]C \rightarrow \infty[/tex].

I don´t know if the problem is positively probable, or if there exist a counter example.

best regards
rayo
 

Related to How Does Increasing C Affect Trajectories in Lagrangian Mechanics?

1. What is Lagrangian mechanics?

Lagrangian mechanics is a mathematical framework used to describe the motion of particles and systems in classical mechanics. It is based on the concept of energy and uses the Lagrangian function to derive equations of motion.

2. What is the difference between Lagrangian mechanics and Newtonian mechanics?

The main difference between Lagrangian mechanics and Newtonian mechanics is the approach to solving problems. While Newtonian mechanics uses forces and accelerations to describe motion, Lagrangian mechanics uses the concept of energy and minimizes the action of a system to determine the equations of motion.

3. How is the Lagrangian function determined in a problem?

The Lagrangian function is determined by taking the difference between the kinetic and potential energy of a system. It is represented by the symbol L and is a function of the generalized coordinates and their time derivatives.

4. What are the advantages of using Lagrangian mechanics?

One of the main advantages of using Lagrangian mechanics is its ability to simplify complex systems into a single equation of motion. It also allows for a more general approach to solving problems, as it does not require specific knowledge of forces and accelerations.

5. What are some common applications of Lagrangian mechanics?

Lagrangian mechanics has a wide range of applications, including analyzing the motion of celestial bodies, understanding the behavior of pendulums and other oscillating systems, and predicting the dynamics of rigid bodies. It is also used in engineering and physics to study the behavior of systems with multiple degrees of freedom.

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