Catenary Arch

An arch is built out of numbered blocks on a hinged building surface. Once the blocks are correctly positioned over an outline of the arch, the construction is tilted slowly towards the vertical until it is standing. The backboard is then lowered, leaving the arch free-standing. The shape the arch takes is called a catenary. This is the same shape taken (with the apex pointing downward) by a hanging chain or rope. There are two chains hanging from posts on the table, a light one and a heavy one. If the arch is disturbed by touching it lightly, it sways to and fro in the same way the chain moves when disturbed.