1. Feb 22, 2012

### teroenza

My textbook (Taylor, Classical Mechanics) and professor introduced the concept of $\nabla$$_{1}$

to mean "the gradient of the function (potential energy) with respect to the position (x$_{1}$,y$_{1}$,z$_{1}$) of particle 1.

I do not understand this. I am familiar with partial derivatives and gradients with respect to general x,y,and z, but not with respect to a fixed point. I could not find anything from my calculus book to help.

2. Feb 22, 2012

### lugita15

It's not gradient with respect to a fixed point. It's just that the potential energy is a function of both the position of particle 1 and the position of particle 2, so you could write V(x1,y1,z1,x2,y2,z2). When he says gradient with respect to the position of particle 1, he means we should calculate partial derivatives with respect to x1, y1, and z1, not x2, y2, and z2.

3. Feb 24, 2012

### teroenza

Ok so it would be just a regular gradient, but WRT particle 1 means I treat x2,y2,z2 as constants. Thanks

4. Feb 25, 2012

### lugita15

Yes, exactly.