Independence of generalized coordinates and generalized velocities

In summary, Lagrangian mechanics involves studying the functional form of the Lagrangian to derive the Euler Lagrange equations, where the coordinates and derivatives take on their usual roles. The Lagrangian is treated as a function of two independent variables, X and Y, which allows for a more complete analysis. A more detailed explanation can be found in my previous posts on this topic.
  • #1
VVS2000
150
17
TL;DR Summary
I was studying the derivation of the lagrangian formalism from Goldstein's textbook for mechanics and at one point they made a claim that generalized co-ordinates and velocities are independent and the derivative of one with respect to the other is zero.
How can I make sense of this and further how to think of this in the context of phase space diagrams?
 
Physics news on Phys.org
  • #2
This question has been asked a number of times. Lagrangian mechanics analyses the functional form of the Lagrangian in order to derive the Euler Lagrange equations. At which point the coordinates and derivatives revert to their usual role, with one the time derivative of the other.

If you search my recent posts for the text in italics you should find a more complete answer.
 
  • Like
Likes VVS2000
  • #3
PeroK said:
This question has been asked a number of times. Lagrangian mechanics analyses the functional form of the Lagrangian in order to derive the Euler Lagrange equations. At which point the coordinates and derivatives revert to their usual role, with one the time derivative of the other.

If you search my recent posts for the text in italics you should find a more complete answer.
Well you're apparently a P-F galaxy so can you provide the link to your post regarding this topic?
 
  • Like
Likes Dale
  • #4
VVS2000 said:
Well you're apparently a P-F galaxy so can you provide the link to your post regarding this topic?
I've never found a way to do it from my phone.
 
  • #5
PeroK said:
I've never found a way to do it from my phone.
Ok, if not too much trouble, can you explain how they're independent here itself?
 
  • #6
VVS2000 said:
Ok, if not too much trouble, can you explain how they're independent here itself?
You treat them as independent variables and study the functional form of the Lagrangian. In the simplest case you have$$L(x,\dot x) = \frac 1 2 m\dot x^2 - V(x)$$Effectively what you do is say, okay, let's study a function of the form$$L(X,Y) = \frac 1 2 mY^2 - V(X)$$That's perfectly legitimate mathematically.
 

FAQ: Independence of generalized coordinates and generalized velocities

1. What is the concept of independence of generalized coordinates and generalized velocities?

The concept of independence of generalized coordinates and generalized velocities is a fundamental principle in classical mechanics. It states that the equations of motion of a system can be described using a set of generalized coordinates and their corresponding velocities, which are independent of each other.

2. Why is it important to consider independence of generalized coordinates and generalized velocities?

Considering independence of generalized coordinates and generalized velocities allows for a more efficient and accurate description of the dynamics of a system. It also simplifies the mathematical calculations involved in solving the equations of motion.

3. How can one determine if a set of generalized coordinates and velocities are independent?

A set of generalized coordinates and velocities are considered independent if they are not related by any constraints or equations. This means that any change in one coordinate or velocity does not affect the others.

4. Can a system have more generalized coordinates than generalized velocities?

Yes, a system can have more generalized coordinates than generalized velocities. This is often the case when there are constraints present in the system, which reduces the number of independent velocities.

5. What is the significance of the Lagrange equations in relation to independence of generalized coordinates and velocities?

The Lagrange equations, which are derived from the principle of least action, take into account the independence of generalized coordinates and velocities. They provide a powerful tool for solving the equations of motion of a system and can be used to determine the dynamics of a system without explicitly considering the forces acting on it.

Back
Top