The Little Catapult that Could
"Your task over the next two weeks is to build a catapult or catapult-like device"
"Range: 18.25 m"
"base must be no larger than 1 square meter"
Choice phrases from a physics project assignment. The burden was lessened for most people in that we could work in groups, but not having any friends in my physics class (and not being a great team-worker anyway), I was in a group of one. The first week was far too busy so for this past week my father and I worked on-- or rather, he worked on, while I oversaw and explained the project constraints and guidelines, gave input on ideas-- building a small catapult. It was built from a deconstructed baby gate (the wood of the main frame), some metal pieces of something to form a rotation point for the arm, and a jar lid for the spoon. Small, distressingly fragile, but working and finished on time.
Bringing it in to school today though, I was confronted by sophisticated metal and strong wooden springs, frames, etc, surgical tubing and iron counter weights, and several person-high constructions including an immense and working trebuchet. A bit unnerving. Mine was the smallest catapult, made of the weakest materials, and when running test shots I realized that the koosh ball we had to fire would not travel as far as the test weights had been tried at home. If I could not send the koosh at least 14.25 of the 18.25 m required distance (the distance between the opposite side aisles our auditorium), I would only get a 70. Not a decent grade; something had to be done.
Getting an idea from seeing someone else using a bungee cord as a catch mechanism, I switched out the heavy-duty rubber bands I had been using in favor of a bungee cord I keep in my backpack (used for attaching my flute to my bike when coming from or going to school). This was right before my actual, graded shots. The bungee cord, being shorter and stronger than the rubber bands, increased the power of the arm and the distance of the ball-- to about 14 m. Still too short to get anything above 70.
Once everyone had fired though, there was still time to do a few more shots each. I tried using all combinations of the the cord and the three super-rubber bands, but it still wasn't enough. The frame began to warp and creak though.
Finally something occurred to me. I removed all the cord and all the bands but one, which I folded in half. It had already been tied in a figure 8 shape, so now it made a double-banded loop, very short and extremely strong, so much so that I had to pile weights against the frame to keep it from snapping just from the pull-back. The fold must have about quadrupled the force. It was quite a strain on my arm to pull the lever back, too.
I wasn't worried if it broke at this point-- it was my last shot, anyway-- so I let it go. And it soared!
Over people's heads, over the finish line, hitting the far wall about 15 feet up. It could have gone even further if there had been no back wall!
"What the heck did you just do to that thing?!" "That definitely didn't go that far before." "Holy sh**!"
I lost 10 points because it went too far and hit the wall, but I got a 90 and I had the furthest shot of anyone in the class. The little catapult had split down the middle and a piece had been shattered off by the force of the last firing, but it was completely worth it.
"Range: 18.25 m"
"base must be no larger than 1 square meter"
Choice phrases from a physics project assignment. The burden was lessened for most people in that we could work in groups, but not having any friends in my physics class (and not being a great team-worker anyway), I was in a group of one. The first week was far too busy so for this past week my father and I worked on-- or rather, he worked on, while I oversaw and explained the project constraints and guidelines, gave input on ideas-- building a small catapult. It was built from a deconstructed baby gate (the wood of the main frame), some metal pieces of something to form a rotation point for the arm, and a jar lid for the spoon. Small, distressingly fragile, but working and finished on time.
Bringing it in to school today though, I was confronted by sophisticated metal and strong wooden springs, frames, etc, surgical tubing and iron counter weights, and several person-high constructions including an immense and working trebuchet. A bit unnerving. Mine was the smallest catapult, made of the weakest materials, and when running test shots I realized that the koosh ball we had to fire would not travel as far as the test weights had been tried at home. If I could not send the koosh at least 14.25 of the 18.25 m required distance (the distance between the opposite side aisles our auditorium), I would only get a 70. Not a decent grade; something had to be done.
Getting an idea from seeing someone else using a bungee cord as a catch mechanism, I switched out the heavy-duty rubber bands I had been using in favor of a bungee cord I keep in my backpack (used for attaching my flute to my bike when coming from or going to school). This was right before my actual, graded shots. The bungee cord, being shorter and stronger than the rubber bands, increased the power of the arm and the distance of the ball-- to about 14 m. Still too short to get anything above 70.
Once everyone had fired though, there was still time to do a few more shots each. I tried using all combinations of the the cord and the three super-rubber bands, but it still wasn't enough. The frame began to warp and creak though.
Finally something occurred to me. I removed all the cord and all the bands but one, which I folded in half. It had already been tied in a figure 8 shape, so now it made a double-banded loop, very short and extremely strong, so much so that I had to pile weights against the frame to keep it from snapping just from the pull-back. The fold must have about quadrupled the force. It was quite a strain on my arm to pull the lever back, too.
I wasn't worried if it broke at this point-- it was my last shot, anyway-- so I let it go. And it soared!
Over people's heads, over the finish line, hitting the far wall about 15 feet up. It could have gone even further if there had been no back wall!
"What the heck did you just do to that thing?!" "That definitely didn't go that far before." "Holy sh**!"
I lost 10 points because it went too far and hit the wall, but I got a 90 and I had the furthest shot of anyone in the class. The little catapult had split down the middle and a piece had been shattered off by the force of the last firing, but it was completely worth it.