Proof of Efficiency of Trebuchet Document
Project:
The goal of our project was to make the best trebuchet that fired a seven gram clay ball the farthest. Our trebuchets were built out of wood since we had limited materials. Also, it had to be less than one meter long in any direction, so vertically, horizontally, and diagonally. The power source was also very limited since rubber bands gave off the most power.
Design:
Our design was no different than the rest, two supports, an axle, and an arm to throw the clay. However, ours was different because we were the only ones to use a spring to power ours. We attacked the spring to one side of the arm held in place by a nail and then attached it to the base with another nail.
In the beginning, our trebuchets arm hit our base after firing so we had to put a stopper up on the top of the two supports. After testing our trebuchet, we decided that it would be better to raise it up in the air more for two reasons. One was to be able to take off the stopper which split one of our supports and two was to get more distance.
As I said we split one of our supports so we ended up just finding another beam of wood and made two new supports. With the improved arms we also had to make a new axle, which also split. Luckily though, it was on our last testing so it didn’t effect us that much. We just got another half inch stick, cut it, and sanded it for less friction. Now our trebuchet was ready to be fired.
Lastly, since our trebuchets arm was now raised, we were able to increase our strings length to 20cm. The nail that we fired it from was ten degrees backwards. This angle let us get even more distance.
Our trebuchet in the beginning only fired at best 20.5m using the spring. We also tested a 1kg weight and two long rubber bands. The weight, well didn’t work at all reaching a maximum distance of 1m. The two rubber bands got to 15.5m and maybe more with more rubber bands, but we couldn’t find any more that matched our original two. In the end though, after making all of the modifications, we got it to reach 32m.
Calculations:
dhoriz=27m, 88.5ft Our ball went 27m through the air before hitting the ground.
dvert=4.42 m, or 14.5ft How high the clay ball went into the air.
tin air=1.9 s How long the clay ball was in the air.
Vhoriz=14.21 m/s, or 31.7mph How fast the ball went horizontally.
Vvert=4.65 m/s or 10.4mph How fast the ball accelerated into the air.
Vtotal=14.91 m/s, or 33.35mph How fast the ball was going both vertically and horizontally.
Angle of Launch: 18.12” The Angle at which the string came loose from the nail.
K (Spring constant): 125 N/m How much force the spring that we had exerted over 1m.
PEspring=9 J The amount of energy the spring had before firing, so about 6.6 foot pounds.
KEball=0.78 J The amount of energy the ball had right before it hit the ground.
% Energy Transfered=9% How much energy was transferred.
Reflection
Over the course of this project, I feel like my group and I all contributed to a great final product. Our trebuchet fired at a pretty good distance of 32meters and used a different power source then we expected. In the begining we were planning on using a rubber band, but after doing multiple tests with different power sources, we found that a spring was actualy the best choice. So we went with it and made our trebuchet. In the end, I thought I had my best group so far and wouldn't have changed anything.