hi, I am an experienced programmer and both OpenGL and C++ belong to my skills. Also, I already have an idea for that scene. My suggestion would be showing a sphere attatched to a pendulum or a block attatched to a spring. This way you would show the simple, yet very interesting, example of harmonic motion. Besides, you would have something less trivial than spheres hitting each other. By the way I have something like a spring already implemented in OpenGL.
Moreover, the extension of the spring could be controlled interactively. And just to add more realism, the oscillation could be damped (the oscillation has its amplitude progressively reduced until it ceases completely). If you're interested PM me, because I know exactly how to do all this. And of course, if you want proof of my skills with openGL, I can send you one or more programs (demo version) I've developed by using OpenGL.