# Homework Help: What is tension in stat mech?

1. Mar 14, 2008

### ehrenfest

1. The problem statement, all variables and given/known data
My stat mech book does a problem where it calculate this quantity F for a system of particles restricted to move in one dimensions using the equation $F = \frac{\partial A}{\partial L}$ where A is the helmholtz free energy. What I am confused about is that I thought F represented tensions, and does tension make sense when you have just a collection of particles moving in 1D i.e. I thought tensions only made sense in the context of strings?

2. Relevant equations

3. The attempt at a solution

2. Mar 15, 2008

### Edward G

The first law of thermodynamics states that

U = dQ + dW (depending on how you define it)

The dW can be replaced with fdL as a unit of work and when the Helmholtz free energy is differentiated with respect to L at a constant temperature, you get the result for the tension.

The system of particles interact with each other, and moving them from the equilibrium position requires a force, as they will try and return to the equilibrium and this is the tension.