Hi guys. I hope this is the right thread for my question. The question is for my project and I can assure you it's not my homework. I know the solution to my problem isn't that complicated but I just lost my self with the problem and I don't have any one to talk with about my problem.(adsbygoogle = window.adsbygoogle || []).push({});

Anyhow, here is my problem. I need to find the forces between two rods. Each rod is constructed from 3 particles (O--O--O) and the potential between the rod is given by:

[tex]U = f(\bar r) \cdot g(\bar u_1 - \bar u_2) [/tex].

Where

[tex] \bar r = \bar r_{22} - r_{21} [/tex]

That is, [tex] r [/tex] is the distance between the two middle particles. [tex] \bar u_i [/tex] is give by

[tex] \bar u_i = \bar r_{i3} - \bar r_{i1} [/tex]

which means it is the vector that shows the direction of the rod. I need to find forces between the particles:

[tex] F = \frac{dU}{dr} [/tex].

My problem is with the derivative of [tex] \bar u_1 - \bar u_2 [/tex] with respect to [tex] \bar r [/tex]. I tried several ways but I alway end up with [tex] \frac{du_1}{d \bar r} - \frac{du_2}{d \bar r} [/tex].

What have I missed?

Thanks.

**Physics Forums - The Fusion of Science and Community**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Expressing start of a vector using a point on the vector

Loading...

Similar Threads - Expressing start vector | Date |
---|---|

I Correct notation for some functional expressions | Feb 17, 2018 |

I Need Aproximate expressions for : ln(x) and 1/ln(x) Thanks | Nov 1, 2017 |

B How to build an equation or expression? | Jul 15, 2017 |

B How Far is Mile Start Line from Finish Line at end of Lane 8 | Feb 3, 2017 |

**Physics Forums - The Fusion of Science and Community**