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This is not a treatise on optics or the index of refraction. It is merely a demonstration that will surprise and engage many of your students. We have all put a pencil in a beaker of water and observed how it appears to bend.1 Not so much fun or engaging, is it? Why not illustrate this optical effect by taking your students spearfishing? Simulated spearfishing, to avoid the financial and legal ramifications. I intercepted a quiver of 30-in long aluminum shaft arrows that were on their way to the dumpster because, if for no other reason, my office could always use more junk in it. The arrows had part of the fletching missing and dull target points, which made them ideal for this project. I stripped the remaining fletching and adhesive from the shaft, made a facsimile of a speargun, and took the students spearfishing. Here is how to make your own speargun. Obtain a 3-ft piece of pine (1 × 4 in) and a pack of screw eyes (#14 × 1−1/16 in) with approximately 3/8-in inside diameter eyes at your local home improvement store. I chose the 3/8-in eye size because the diameter of the arrow shafts was 0.30 in. Yours may be different. Lay out the pattern in Fig. 1 on the pine board, cut it out, then round and sand the edges smooth. Insert the screw eyes along the top edge at about 1, 4, 9, and 20 in from the front end of the speargun. Make sure that the eyes all line up since the arrow is powered by gravity alone and must slide through the screw eyes freely (like an arrow through Penelope's 12 axe heads).



This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in

Trikosko, W. (2014). Shooting Fish in a Barrel: A Demonstration of the Refraction of Light. The Physics Teacher, 52(6), 367–367.

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