vpython

=VPython for Modeling Matter=

VPython is a programming language with a module that allows you to view the objects that you create. By using a loop you can perform many iterations of Newtonian calculations to simulate the motions of objects subject to classical interactions. The language is open-source and available for download at [|vpython.org].

KineticsKit Module
A module to simplify the modeling of solids is available for download at []. The KineticsKit was developed by Markus Gritsch as a way to create a 3D ball and spring array without writing many tedious lines of code. I have found it works well in PC versions of VPython but is tough to install with the Mac version. There are many example programs at the bottom of the KineticsKit page.

Modeling a Diatomic Molecule
I am in the process of writing a program to show two models of a diatomic molecule. The program uses a Hooke's Law approximation for one molecule and a force derived from the U=(a/r^9)-(b/r) energy function for the other. When you choose "a" and "b" values the program automatically approximates the value of "k" that would result from looking at the third term of a Taylor expansion of the associated energy function. The force is found from the negative gradient of the energy function. When I am done I will also include a scale to show the equilibrium position. Ultimately I want to use this program to show that the Hooke's Law model does not predict thermal expansion. I will show this by having the moving molecule leave a trail which will become more dense as the object spends more time at that position. Please feel free to make suggestions about the program.

The program in its current state can be downloaded:



Here is a second version of the program where the particles leave dots at equal time intervals. The distribution of dots gives you a sense of the average separation of the particles. This shows that more energy (higher temperature) leads to expansion.