SimKit
 
SimKit is an interactive simulation program for mechanical interations. The object oriented framework of the program has been written by David Baraff who is an adjunct professor at Carnegie Mellon University, currently working for Pixar studios. I ported the framework to the PowerMac and added interactive functions to the simulation program. (The original Silicon Graphics application was not interactive.) To the right you can see a screen-shot of the PowerMac application.

You can create any (polygon-based) shapes, specify the mass (or density), choose global behaviors (such as "can rotate", "can move", "affected by gravity", etc...") and assign static and dynamic friction coefficients to them. Shapes can also be joined, and the gravity center of an object can be moved around.

You then can add joints between shapes or nails that pin the object against the background. You can also specify that objects can only move between two parallel lines, etc... Springs can also be added to the system, and rest length, spring constant and damping factor can be specified.

There are also active components that can be added to the system. Rotating motors (you can specify the speed and maximum force) and shrinking/expanding motors can be placed in the system.

Then turn on gravity, dynamics and friction, and watch your system evolve. Of course you can apply forces on objects with the mouse during the simulation.

Editing is made easy with snap-to grid and zooming functions. A special camera mode lets you follow a moving body around. Some limited sound-features can be used to signal collisions.

At this moment, only rigid objects are supported. Nevertheless, deformable shapes can be simulated though small rigid bodies connected with springs. Unfortunately, this technique can result in very time-consuming calculations.

I have also written a small demo program called GeoKid based on the same framework. It's basically an application that allows you to place squares, triangles and other 2D forms on a table, apply forces to them, and watch the system evolve. You can also turn gravity or friction on and off.

If you want to check it out, click here (about 235k, bin-hexed). It only runs on the PowerMac, since it is a very computing-intensive application. If your Mac slows down too much, be sure that you are running in 256 color mode and try turning friction off. GeoKid does not run on Intel Macs.