The goal of this project, Fire Away!, was to create a trebuchet that could throw an object as many meters as possible, with the best possible outcome. The trebuchet has to stay in one place and be able to be used over and over without breaking. It also must have two arms that hold the lever arm and must be smaller than 1 meter in all directions to be easy to carry by a single person. Some of the most important parts I paid attention to was the size of the trebuchet. Because we could only have the trebuchet less than 1 meter, we had to figure out a way to give the trebuchet lots of power. Luckily, we were able to fit lots of rubber bands on the trebuchet to give it more power.
Our original model compared to our final model had many changes.
•For one, the nail that connects the rubber bands to the base board used to be at an angle and nailed in on the top of the board. But, after the nail kept becoming loose and detaching, we found that there was more tension against the rubber bands when the nail was nailed to the side of the board. Therefore we moved the nail to the side.
•Another modification was the angle of the nail that hooked the string of the ball. It was found that the ball would leave the trebuchet at around a 45 degree angle if the nail was at a 0 to -10 degree angle. Therefore, we pushed the nail in more straight to make the ball go less high.
•We also changed the axle from 4 small sticks to 1 strong wooden stick. This is because, under pressure, the 4 sticks cracked from the force of the rubber bands.
•Because the axle tended to come loose from the arms, we overlapped a rubber band on the outside part, where the axle and arms meet, to keep it from sliding out.
•For the clay ball, we changed the weight to 7 grams because when multiple clay ball sizes were tested, it was found that the ball that went the furthest was 7 grams. Ours was originally only slightly larger than this.
•The last modification we made was the length of the string connected to the clay ball. Each time we tested the trebuchet, we would be changing the string length in order to reshape the ball. We didn’t realize that this was changing our outcome. Therefore, we decided to have our string length 40 cm based off tests.
When using rubber bands, the projectile traveled a further distance than when multiple 1kg masses were used. The question my group was testing was; rubber bands or weights? We wanted to figure out if it was more scientifically correct to use rubber bands over weights or the other way around to fire a trebuchet. Along with the science of it, we needed to take note of which was easier and more efficient to use. Before we could actually test the launch of our trebuchet, we needed to decide on masses and rubber bands. We needed to know what the force of the rubber bands was in comparison to the force on each weight. Surprisingly, by using a spring scale to measure the force/spring constant of the rubber bands, we found that one rubber band has a force of 10 Newtons while one 1 kg weight also has a force of 10 Newtons. Therefore we figured that they should cause the projectile to launch the same distance for one rubber band and 1 kg weight. Oddly, we found that this was not the case. Theoretically, they should launch the projectile the same distance because the weights and rubber bands caused the same force, but other variables were not allowing this to happen. The big reason was the efficiency of rubber bands. When we placed 1 rubber band on the attaching nail, it was easier to slide on and it stayed on, but when we placed a weight on, it took up a lot of space and swung a bit. Therefore, when the trebuchet was released, the weight swung down and bounced around a bit. It caused the arm to not have an immediate snap that cause the projectile to really go far. From one weight we were only able to get a distance of 1 meter while with one rubber band we got a distance of 4 meters. We continued to increase the amount of rubber bands and weights, but while we were able to go up to at least 8 rubber bands, we could barely fit 3 weights on the nail. At 3 rubber bands, we were able to get a distance of 11 meters while with 3 weights we could only get a distance of 4 meters. We concluded that rubber bands are a more efficient way to set off a trebuchet and that force is not a variable in this case, but potential energy is. The factor that needs to be changed is how many rubber bands there are and how far they are stretched. Or with weights, how many weights there are and how high they are released from. The issue with weights is they are not efficient. Even if one weight equals the force of one rubber band, it does not matter. This is not a problem of force but a problem of potential energy. The more potential energy, the better.
Our original model compared to our final model had many changes.
•For one, the nail that connects the rubber bands to the base board used to be at an angle and nailed in on the top of the board. But, after the nail kept becoming loose and detaching, we found that there was more tension against the rubber bands when the nail was nailed to the side of the board. Therefore we moved the nail to the side.
•Another modification was the angle of the nail that hooked the string of the ball. It was found that the ball would leave the trebuchet at around a 45 degree angle if the nail was at a 0 to -10 degree angle. Therefore, we pushed the nail in more straight to make the ball go less high.
•We also changed the axle from 4 small sticks to 1 strong wooden stick. This is because, under pressure, the 4 sticks cracked from the force of the rubber bands.
•Because the axle tended to come loose from the arms, we overlapped a rubber band on the outside part, where the axle and arms meet, to keep it from sliding out.
•For the clay ball, we changed the weight to 7 grams because when multiple clay ball sizes were tested, it was found that the ball that went the furthest was 7 grams. Ours was originally only slightly larger than this.
•The last modification we made was the length of the string connected to the clay ball. Each time we tested the trebuchet, we would be changing the string length in order to reshape the ball. We didn’t realize that this was changing our outcome. Therefore, we decided to have our string length 40 cm based off tests.
When using rubber bands, the projectile traveled a further distance than when multiple 1kg masses were used. The question my group was testing was; rubber bands or weights? We wanted to figure out if it was more scientifically correct to use rubber bands over weights or the other way around to fire a trebuchet. Along with the science of it, we needed to take note of which was easier and more efficient to use. Before we could actually test the launch of our trebuchet, we needed to decide on masses and rubber bands. We needed to know what the force of the rubber bands was in comparison to the force on each weight. Surprisingly, by using a spring scale to measure the force/spring constant of the rubber bands, we found that one rubber band has a force of 10 Newtons while one 1 kg weight also has a force of 10 Newtons. Therefore we figured that they should cause the projectile to launch the same distance for one rubber band and 1 kg weight. Oddly, we found that this was not the case. Theoretically, they should launch the projectile the same distance because the weights and rubber bands caused the same force, but other variables were not allowing this to happen. The big reason was the efficiency of rubber bands. When we placed 1 rubber band on the attaching nail, it was easier to slide on and it stayed on, but when we placed a weight on, it took up a lot of space and swung a bit. Therefore, when the trebuchet was released, the weight swung down and bounced around a bit. It caused the arm to not have an immediate snap that cause the projectile to really go far. From one weight we were only able to get a distance of 1 meter while with one rubber band we got a distance of 4 meters. We continued to increase the amount of rubber bands and weights, but while we were able to go up to at least 8 rubber bands, we could barely fit 3 weights on the nail. At 3 rubber bands, we were able to get a distance of 11 meters while with 3 weights we could only get a distance of 4 meters. We concluded that rubber bands are a more efficient way to set off a trebuchet and that force is not a variable in this case, but potential energy is. The factor that needs to be changed is how many rubber bands there are and how far they are stretched. Or with weights, how many weights there are and how high they are released from. The issue with weights is they are not efficient. Even if one weight equals the force of one rubber band, it does not matter. This is not a problem of force but a problem of potential energy. The more potential energy, the better.
Physics Concepts
Reflection
Over the course of this project, we had to really work efficiently, due to lack of time. I feel my group did this really well considering the amount of time. We were able to finish everything before presenting even with some mistakes or needing to re-test. I also feel work ethic was a strong category for this project. Everyone wanted to help in some way through out the project and it really improved our team work skills.
All though I do not have many negatives for this project, my group could have done a better job on sharing ideas. I feel that we didn't brainstorm better ideas before actually starting the project. I also think everyone could have had a little more leadership instead of only some people taking action.
Over the course of this project, we had to really work efficiently, due to lack of time. I feel my group did this really well considering the amount of time. We were able to finish everything before presenting even with some mistakes or needing to re-test. I also feel work ethic was a strong category for this project. Everyone wanted to help in some way through out the project and it really improved our team work skills.
All though I do not have many negatives for this project, my group could have done a better job on sharing ideas. I feel that we didn't brainstorm better ideas before actually starting the project. I also think everyone could have had a little more leadership instead of only some people taking action.