Bow & Arrow A bow and arrow provides an excellent example of energy transfer. Where is the energy stored in the ancient system? As the bow is released, where might the energy transfer? Image from Wikipedia Commons
Crossbow Archaeological evidence places the invention of the crossbow in ancient China. Its principle was basically the same as the bow and arrow except it could store more energy, and maintain that energy with little effort, allowing for better aim. Based on your observations why might this be the case? Drawing of a crossbow by Leonard daVinci. Image from Wikipedia Commons
Early Catapults The first spring catapults were essentially big crossbows, making it possible to store even more energy and hurl larger projectiles. Oxybeles, from Ancient Greek Artillery Technology from Catapults to the Architronio Canon, by Michael Lahanas. Online at http://www.mlahanas.de/Greeks/InventionsC.htm
Catapults Evolve Military engineers continued to improve catapults so they could throw heavier projectiles further. This ballista catapult uses torsion springs made of animal sinew. Roman Ballista by Vissarion, from Wikipedia Commons
Early Design Variables Instructional manuals from early Greek and Roman engineers were highly detailed showing the construction process for catapults that were the lightest possible device to hurl the largest projectiles as far as possible. What might one infer from these detailed manuals about their use of variables? Detailed information on the development of the catapult from Soedel, Werner and Foley, Vernard (1979). Ancient catapults. Scientific American, March 1979, pp. 150 – 160. Image from Wikipedia Commons
Control of Variables It is likely that the method of controlling variables evolved from efforts to refine various technologies, from catapults to weaving and dying fabric. Yarn drying after being dyed in early American tradition, at Conner Prairie living history museum in Fishers, Indiana. Photo shot by Derek Jensen (Tysto). Image from Wikipedia Commons.
Engineering and Inquiry Today we usually think of control of variables as a method for conducting a scientific inquiry. It bears keeping in mind that this method evolved in association with the desire to improve technologies. How might you challenge your students in the classroom to link scientific inquiry and the design process with control of variables?