Algodoo

How is the mechanism triggered? I don't see much code at all.

Examining the code using either of my Code Extractors shows:

scene.my.SpringLength = 0.316271;

Scene.addPolygon {
    onCollide := (e)=>{
        scene.my.SpringLength = 0.10000000
    };
    pos := [-8.5651327e-006, -0.0054667774];
};
Scene.addSpring {
    length := {
        scene.my.SpringLength
‭‡â€‡â€‡â€‡};
};

The polygon is the saw blade and the spring is the brake bar spring. The spring acts as an actuator by getting shorter upon finger contact with the saw blade.