Algodoo

While trying to figure out how this scene: Spring Car works, I eventually realized that it is powered by nothing more than an unstable spring! Every Algodoo spring has a parameter called "Damping", and it is normally used to reduce jitter or oscillations. But if you make the value negative instead of positive, then it has the opposite effect by making the spring unstable. If you make the value high enough, then the spring starts to generate its own jitter and oscillations.

This simple scene demonstrates that behavior. Through trial and error, I found values of damping and spring constant (strength) that creates a slightly unstable system when a ball bounces on the beam. If the values get out of balance in either direction, either the instability smooth's out, or it gets so bad that the mechanism fly's apart!

Start Algodoo and then play around with different spring values and/or ball mass values. Be careful that you make very small changes at a time.