To make clay beams, start by working the clay to make it pliable. To make the large beam, set the 1-by-1 removable mold piece against the stops and stuff clay into the mold as tightly as possible. Using your knife or metal rule, smooth down the top of the clay so that it is even with the top edges of the mold. Then, keeping the removable mold and clay together, turn over the mold and reset it between the stops. You will see some unfilled holes in the bottom of the clay beam. Stuff more clay in to fill these holes and smooth down the clay so that it is even with the top edges of the mold again. Lift the moveable mold and clay and pull apart the wood pieces. You now have a 1-inch-by-1-inch clay beam. You can trim it to the length that you want for various purposes.
Making the small beam is very similar to making the large one. The only thing to look out for is that the screen mold has one edge that is rounded rather than square. That edge should be set against the stop in order to get the proper -inch-by--inch beam.
To do the demonstration with the beams you make the big beam four times as long as the small beam. This maintains the constant linear proportion of 4 to 1. You want to choose lengths that clearly show the difference in rigidity of the two scales. We usually make the small beam about 6 cm long and the large beam about 24 cm long. The length that works best for you will depend on the consistency of your clay, how much it has been handled, and the temperature of the room where you are working. Experiment and see what works best.
Make or have your students make enough beams so that each group of no more than eight students can have a large one and a small one. Ask your students to compare the two beams.
This demonstration shows in a very concrete manner the fact that when you scale up proportionally (i.e., keep things the same shape but change the size), weight increases faster than strength.
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