Solving Work Along a Force Field Path - A Math Question

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Discussion Overview

The discussion revolves around determining the path of travel of a particle in a varying force field, particularly focusing on the mathematical aspects of work along a curved path and the application of the Lagrangian formulation in classical mechanics.

Discussion Character

  • Exploratory
  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • One participant notes that work along a curved path is represented by a line integral and questions how to determine the path of travel when the force varies at each point in space.
  • Another participant suggests that the Lagrangian formulation of classical mechanics can be used to find the path by writing the Lagrangian and solving the Euler-Lagrange equation with initial conditions.
  • A later reply reiterates the use of the Lagrangian formulation and expresses relief that the solution is not overly simplistic.
  • Another participant proposes that for a constant mass, Newton's equation can be solved to find the path of travel, which involves a system of differential equations.
  • One participant introduces the concept of conservative force fields, stating that in such cases, the line integral is constant for any path and depends only on the initial and final points.

Areas of Agreement / Disagreement

Participants express different approaches to the problem, with some focusing on the Lagrangian formulation and others on Newton's equations. There is also a distinction made regarding conservative force fields, indicating that multiple competing views remain without a consensus.

Contextual Notes

Some assumptions about the nature of the forces and the conditions under which the equations apply are not fully explored, and the discussion does not resolve the complexities involved in varying force fields.

marschmellow
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This might be more of a mathematical question, but the other day in Physics my teacher said that work along a curved path is a line integral, which made perfect sense to me. But then I wondered how one determines the path of travel if the force varies at each point x, y, and z. So how would you find the path of travel of a particle given a vector field of forces, an initial position and an initial velocity?
 
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This is exactly what the Lagrangian formulation of classical mechanics is for. Basically you write the Lagrangian, solve the Euler-Lagrange equation, plug in your initial conditions and you have your answer.
 
DaleSpam said:
This is exactly what the Lagrangian formulation of classical mechanics is for. Basically you write the Lagrangian, solve the Euler-Lagrange equation, plug in your initial conditions and you have your answer.

Okay good, that sounds hard. I'm glad the answer wasn't something really obvious, because I would be embarrassed for asking.
 
marschmellow said:
This might be more of a mathematical question, but the other day in Physics my teacher said that work along a curved path is a line integral, which made perfect sense to me. But then I wondered how one determines the path of travel if the force varies at each point x, y, and z. So how would you find the path of travel of a particle given a vector field of forces, an initial position and an initial velocity?

For a point-like (constant) mass all you need is to solve Newton's equation:
[itex] \mathbf{F}(\frac{d \mathbf{r}}{dt},\mathbf{r},t)=m\frac{d^2 \mathbf{r}}{dt^2}[/itex]
which is a system of 3 differential equations, the unknown is [itex]\mathbf{r}[/itex], the 'path of travel' (parametrized by time)
 
This maybe slightly off base with what you are talking about but incidentally, if your force field is conservative ( ie the force at any point depends on a function of position, like gravitational and electrostatic forces do ) then the line integral will be a constant for any path you choose and will depend only on your initial and final points.
 

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