Beam bridges
These bridges are made up of balls joined by elastic links. When the links are compressed they are drawn in red - or yellow under greater compression. Under tension the supports are drawn in blue.
What are the forces (compression or tension) in different parts of the bridge - and how do they keep the bridge standing?
How do these forces change when the bridge is under load? (try dropping the brick or just pull the bridge with the mouse)
How do the short and long bridges (but same thickness) differ in their behaviour?
What forces do the bridges exert on their supports?