Look at the hanging chain. Each link of the chain has two opposing forces - gravity is pulling down and the links above (and the supporting eye bolt) are pulling up.If these forces are not in balance what would happen? How flexible is the chain? If you push on a link, the chain easily moves from side to side. So if the opposing forces of gravity pulling down and the eye bolt pulling up are not exactly in balance, the chain will shift from side to side until these forces are in balance.
Therefore nature is using the chain to show us a pattern (or curve) that will balance these opposing forces.
On the LAYOUT BOARD is a pattern copying the curve of the hanging chain. There are also twenty-one blocks of wood that when assembled correctly will match the curve of the hanging chain.
To begin building the arch, first make sure the HINGED BASED is pivoted up against the LAYOUT BOARD.
Notice that each of the blocks has a blank side. That side must be on the inside of the arch. Notice that one end of each block has a solid line. That solid line must be towards the HINGED BASE. The ends of the blocks are cut at very particular angles. The blocks must be positioned according to these rules so that they create the drawn pattern. 
Assembling the blocks is easiest if one starts in sequence with block number one. Place all of the blocks on the LAYOUT BOARD pattern. Check to make sure that the blank side of each block is towards the center of the arch and that the end of the block with the solid line is towards the HINGED BASE.
Standing the arch up is easiest if there is one person on each side lifting the LAYOUT BOARD. Use a couple fingers of one hand to hold the HINGED BASE against the LAYOUT BOARD. With the other hand grab the wire loop. Slowly raise the LAYOUT BOARD while keeping the HINGED BASE tight against the bottom of the LAYOUT BOARD. When the LAYOUT BOARD is vertical each person should use one hand to hold the HINGED BASE firmly against the table top. Then slowly lower the LAYOUT BOARD. The arch should stand.
The arch is self-supporting, meaning it is supporting its own weight. There is no coating of any kind on the blocks - they are bare hard maple.
The name of the shape of the hanging chain (and the wooden arch) is a catenary curve. According to the History of Mathematics Archive www-groups.dcs.st-and.ac.uk:80/~history the originator of the term "caatenary" was Huygens in a letter in 1690. The equation for the "chain curve" was obtained by three mathematicians, Leibniz, Huygens and Johann Bernoulli in 1691 in response to a challenge by Jabob Bernoulli.
The St. Louis Gateway Arch is another example of this curve.
Most arches in walls and buildings have curved tops and straight sides. The curved top is usually a semi-circle but sometimes is half of an ellipse. These arches cannot be built of a single row of blocks. These arches almost always require a form of glue between the blocks - mortar. They also require thick side walls to keep the arch standing.
(CAN ANY OF THE READERS IDENTIFY WHAT IS THE GENERAL SIGNIFICANCE OF THE KEYSTONE IN ARCHES? HOW MIGHT THAT RELATE TO THIS EXHIBIT?)
A student could collect pictures of arches and compare and contrast them. How many have straight sides and how many have curved sides like this arch? How many have semi-circular arches and how many are parts of an ellipse? Compare these with pictures of the cables on suspension bridges, hanging telephone and electricity cables, hanging ropes, et cetera.