# Homework Help: Yukawa potential energy function

1. Sep 18, 2010

### astenroo

1. The problem statement, all variables and given/known data
This is not yet an attempt at solving a problem. I just need confirmation on that I'm on the right track. So, I am supposed to derive an expression for the radial force function from the given Yukawa-function.

2. Relevant equations

U(r) = -(r/r0)U0 exp-(-r/r0)

3. The attempt at a solution

I'm thinking about two possibilities here. First: Derivation of said function with respect to r (normal differential). Second: Partial differentiation to solve for the gradient (although I think this is not necessary since r is a fixed value, and no coordinates are given in the context of the problem)

2. Sep 18, 2010

### RoyalCat

3. Sep 18, 2010

### astenroo

Ah true, since this function only has one variable which is r. What I am a bit concerned about is that if the system for spherical coordinates should be used in this derivation... Or they aren't needed since the radial force is dependant only on r (in this given situation)?

4. Sep 18, 2010

### RoyalCat

It doesn't matter, you have only one axis specified in the problem, and that's the radial axis. The way to take the gradient with respect to the radial axis is $$\frac{\partial f}{\partial r}\hat r$$
It doesn't matter what the other two axes are.