This week we made and tested arch bridges. First we tested a flat card bridge. It couldn't even hold a single weight. So to make it stronger we put an arch underneath and placed weights on top again. It held 160g.
We decided to increase the number of arches to two. This time it held 360g.
I found this excellent website which explains how to make a huge arch. Maybe we will have a go at this soon. In the meantime we will try the arch bridge at the science centre.