She started off building a house but I convinced her it would be more fun to let Daddy build a suspension bridge instead. I can't think of a better way to see tension and compression.
Version 1. main span 420mm
So we built a bridge using lego, some thread and Plarail tracks.
Amazingly it was able to hold a 400g train despite the towers not being properly anchored to stabilize the lateral forces.
So I got thinking about the limitations of the design and bought some better thread and 'popsicle sticks' at the craft shop downstairs, and we built a 2nd version on the floor of the lounge,
Version 2. main span 840mm, towers 290mm high
This version is cable-stayed design, with strings going through 3 beams each made of 3 popsicle sticks glued together, and anchored to the floor with Sellotape. The 4 tracks were stuck to the beams and towers using blu-tack which made it less fragile.
This design has 2 cables per side no trouble bridging 800m, which made me curious how long we could make it. So I cut some longer strings and next weekend we made another.
Version 3: main span 1,266mm, 2,100mm
This time I anchored the strings to the floor using popsicle stick beams spaced apart in a classic cable-stayed pattern. This made it easier to adjust the tension.
Hannah suggested joining the cables together with Sellotape in the middle to stop the track dipping when the train passes across.
The bridge easily bridged the 1,200mm river and Daddy regretted not cutting strings long enough to try a 8 track (1,700mm) version. But by this point Hannah had long since lost interest.
Video : Bridge Project
I had to nag Hannah to do the narration for this video to take to school. The idea was to film shots of Hannah demonstrating the construction in reverse order and we edited them together 'backwards'.
