Bridges, cranes and roofs stand up because every bar carries its share of the load. In this simulator you build a truss from bars and joints, add loads and supports and find out whether it holds or collapses. Each bar is colored by the force it carries, red for tension and blue for compression, and the reactions at the supports are shown as well. Try a triangle and a square with the same load and you will see at once why triangles are everywhere in structures. It is a quick way to test ideas before building a model with sticks or straws.
