Generalized coordinates and the Lagrangian

  • #1
GLD223
14
7
Homework Statement
Find the degrees of freedom of the system with the given PE. What are the variables of integration? Find the Lagrangian using the generalized coordinates.
Relevant Equations
##PE = 1/2 * k_1 * R^2 + 1/2 * k_2 * (\vec{r} - vec{r_1})^2## note that ##r## and ##r_1## are vectors
So I think the mass can only move in two "coordinates" the axis of which the mass is connected to ##k_1## and the axis connecting it to ##k_2##. Therefore, the D.O.F is 2. I don't understand what it the meaning of "variables of integration" What does it mean?
Apart from that, I attempted to solve for the Lagrangian:
##T = 1/2 * m * v_m^2##
V is given
##v_m = d/dt(x_m)##
##x_m = 1/2 * \vec{r_1} + something* \hat{y} = 1/2 * r_1 * \hat{x} + something* \hat{y}##
I have no clue how to solve this. Any help would be appreciated
 

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  • #2
Hi,
The problem statement is a complete mystery. No idea what ##R## is, nor what ##\vec r## is. Is ##\vec r_1## fixed? Given?

Sort out your notation. V is given means V=PE ?

##x_m## ? "##something##" ?

##\ ##
 
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Related to Generalized coordinates and the Lagrangian

1. What are generalized coordinates?

Generalized coordinates are a set of independent variables that describe the configuration of a system. They are used to uniquely specify the position of each particle in the system without the need to reference fixed coordinate axes.

2. How are generalized coordinates related to Lagrangian mechanics?

In Lagrangian mechanics, generalized coordinates are used to describe the configuration of a system in terms of its degrees of freedom. The Lagrangian is a function of the generalized coordinates, their time derivatives, and possibly time itself, and is used to derive the equations of motion for the system.

3. Why are generalized coordinates useful in physics?

Generalized coordinates are useful because they simplify the analysis of complex systems by reducing the number of variables needed to describe their motion. They allow for a more intuitive and efficient way to derive the equations of motion using the principle of least action.

4. Can any set of coordinates be used as generalized coordinates?

No, not every set of coordinates can be used as generalized coordinates. They must be independent and uniquely describe the configuration of the system. Additionally, they should be chosen to simplify the equations of motion and make the analysis more manageable.

5. How do you determine the Lagrangian of a system using generalized coordinates?

To determine the Lagrangian of a system using generalized coordinates, you first need to express the kinetic and potential energies of the system in terms of the generalized coordinates and their time derivatives. The Lagrangian is then defined as the the difference between the kinetic and potential energies, L = T - V.

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