I was a bit mystified by their disappearance until this weekend when I looked out and saw a 4 foot Green Iguana happily munching away at my vines. Iguanas are an exotic invasive species that are now everywhere across South Florida, much to the displeasure of many homeowners. I have always given the iguanas a pass as I do not feel it is their fault they are here, and besides, if all the humans that purposefully invaded had not displaced the natural small herbivores like rabbits and gopher tortoises there would not be this vacated niche that the iguanas fit into perfectly. Note that I do not have the same indifference to invasive exotic predators like the Burmese Python devastating the Everglades, or the uninvited Lionfish that is on our reefs. But I could not stand back and watch this year’s crop of Moonvine being devoured.
But, what to do? I did not want to kill the stupid thing, although it is legal to do so as long as firearms are not employed. Despite their scary appearance, they are rather nonaggressive and not much smarter than the plants on which they dine. I settled upon spanking it with pebbles shot from a slingshot. Each non-lethal hit made the thing sprint about ten feet, so after about twenty shots it had moved off of my property. After every shot the dumb thing looked at me with not one hint of understanding or fear.
It was the slingshot that got me thinking. Growing up here in South Florida, I was surrounded by rivers and hammocks, even though my parent’s house would now be considered to be just outside of downtown Ft. Lauderdale. I was equally drawn to both environments, and while I was allowed fishing rods quite early, my parents were less inclined to let me loose with guns… for good reason as I started many years short of being a teenager.
Instead, I resorted to fashioning my own hunting weapons like hand-made bows and arrows. And I was quite deadly with my ever-present custom slingshot. I, and my friends, hand carved the handles and made our own bands by cutting automotive tire inner tubes. And, thinking back, our desire and competition drove us to be quite creative, like finding that triangular shaped straps worked better. We even customized their length to the “draw” of our particular arm lengths, much like compound bows are custom fitted today.
So, to get back to flyfishing… or actually casting…
I did not realize it then, but I think our experiments were quite intuitively demonstrative to many concepts of springs. The strength of the rubber stock (spring constant k?), potential elastic energy, and oscillation rates being related to k and mass were all parameters we explored and utilized although we had no idea that we were doing so. And there was one observation that stands out in my memory.
At first we thought that if you drew back the bands to the point where they became rigid (elastic limit?) you should get the maximum output. But, we quickly learned that was not the case. Instead, we found that if you drew back not quite to that point, where you still had some play, things got a lot better. And, if you then smoothly accelerated your draw up to but just shy of the stop and cleanly released… well then, you really got some zing! We measured our output by driving a BB through both sides of a soda can so there can be no dispute as to the veracity of our findings!
This memory had the feeling of the saying of “déjà vu all over again”, as I have recently come to a similar conclusion when casting a flyrod. I wish I could write an equation to justify my assumptions, but I am afraid it would likely take another 50 years for me to do so… and I have an upcoming fishing trip to prepare for.