Playing with Lagrangian and I screw up

In summary, the conversation discussed the use of the Lagrangian approach and the importance of treating it as an abstract function of independent variables. It was also noted that textbooks may vary in how they explain this concept.
  • #1
Trying2Learn
373
57
TL;DR Summary
Lagrangian, Kinetic Energy (where am I going wrong)
I am sorry for all these questions this morning.

Could someone read the attached and tell me where I am going wrong?
 

Attachments

  • WhereAmIGoingWrong.pdf
    34.9 KB · Views: 91
Physics news on Phys.org
  • #2
Trying2Learn said:
Summary:: Lagrangian, Kinetic Energy (where am I going wrong)

I am sorry for all these questions this morning.

Could someone read the attached and tell me where I am going wrong?
The Lagrangian approach requires that you treat the Lagrangian as an abstract function of independent variables. You can't jump ahead, solve the equations of motion, and plug these back into the Lagrangian and start again.

It's only when you are solving the Euler-Lagrange equations that you transition from the equations in their abstract form, to the equations that represent a specific solution in terms of a particle trajectory etc.

Text books tend to vary to the extent that they make this distinction clear.
 
  • Like
Likes vanhees71
  • #3
Ah ha!

Thank you!
 
  • Like
Likes berkeman

1. What is Lagrangian and how is it used in science?

Lagrangian is a mathematical function that is used to describe the motion of a system in classical mechanics. It takes into account the kinetic and potential energies of the system and allows for the calculation of the system's equations of motion.

2. What are some common mistakes that can occur when working with Lagrangian?

One common mistake is forgetting to account for all of the forces acting on the system. Another is using the wrong coordinate system or not properly defining the system's constraints.

3. How does Lagrangian differ from Newtonian mechanics?

Lagrangian is a more general and elegant approach to describing the motion of a system compared to Newtonian mechanics. It takes into account all of the forces acting on the system, including non-conservative forces, and can be applied to systems with complex geometries.

4. Can Lagrangian be used in fields other than classical mechanics?

Yes, Lagrangian can also be used in other areas of science such as quantum mechanics and electromagnetism. It provides a powerful tool for understanding the behavior of systems in these fields.

5. How can I improve my understanding and application of Lagrangian?

Practicing with various examples and problems is the best way to improve your understanding and application of Lagrangian. It is also helpful to have a solid understanding of calculus and classical mechanics principles.

Similar threads

  • Classical Physics
Replies
21
Views
2K
  • Classical Physics
Replies
2
Views
929
Replies
19
Views
1K
Replies
1
Views
467
Replies
13
Views
953
Replies
1
Views
607
Replies
7
Views
1K
Replies
22
Views
872
Replies
10
Views
4K
Back
Top