What We Did
The object of this project was to send a projectile as far as possible. We had to construct a device that stayed in one place on the ground and be able to be used multiple times. In our design we had to include an axle that was held up by two legs and have a lever arm with an effort and load end. We had to easily move our trebuchet and no dimension at any point could be more than one meter. Finally, we were only allowed to set and release the lever, we could not do the actual firing.
Modifications
- Our first modification was to raise the legs. The original height was 31cm, which we then added 16.5 cm to, to create a total height of 50.5cm. We found that the higher they were, the farther our projectile went.
- We then decided to change the rod to a thicker, more sturdy one. We did this because our first one was bending under the force of the rubber bands on lever.
- The string that was attached to the projectile was changed to 35 cm. In our experiment we determined what length of string would lead to optimal distance. We tested six string lengths that were all folded in half when we put the clay weight around it. We concluded from our results that a string a length of 35 cm would work the best. When we tested the 30 cm length, it traveled an average distance of 21 meters and when we tried a length of 35 cm it traveled an average distance of 30 meters which was the farthest any of our trials had gone. We decided that this happened because the 30 cm length was too short and hung off of the ground for the majority of the arm’s rotation. We decided that as the string length increased the distance decreased after it past its’ peak of 35 cm. This is because the string is so long it is just dragging on the ground. It is dragging until the arm has completed its’ rotation, which results in the projectile going close to nowhere.
- Our next modification was the amount of rubber bands. At first we had 2 rubber bands. After we changed the height of the legs we had to chain two rubber bands together to actually reach from base to the effort part of lever. After we chained them we added a total of four chains with 2 on each.
- We then changed the nail to a small headed one with a 10° angle when bent. We did this because the projectile came off of the nail at just the right time where it went the farthest and did not fall off too soon.
- We also changed the ratio of effort to load to 1:2. Originally it was slightly under the 1:2 ratio. This was better because the mechanical advantage is greater than one.
- We finally decided to add a bar below the arm to stop it from rotating. We added this as a safety feature because 3 out of our 4 group members got hit by the arm which was not fun.
Calculations
Our projectile traveled a distance of 50 meters, which is equivalent to 164 feet, in 4.5 seconds.
- Velocity Horizontally- You find this by using the equation for velocity which is v=d/t. You use the total time because the total time is horizontally. Our horizontal velocity was 11.11m/s, which is 24.9mph.
- Velocity Vertically- To find this you use the acceleration equation which is a=v/t. You use this to figure out the total velocity. Our velocity was 22.05m/s which is 49.3mph.
- Angle of Release- To find this we use inverse trig of tangent. The equation is θ=tan^-1(opposite leg/ adjacent leg).
- Total velocity- to find this use you the Pythagorean Theorem to find the hypotenuse. In our case we used the number 22.05m/s (vertical) and 11.11m/s (horizontal). That give you a total velocity of 24.7m/s which is the same as 55.3mph.
- Spring Constant- This tells you how easy it is to stretch the spring. The equation is k=F/d. The unit of measure is N/m.
- Distance Vertically- This tells you how high the object goes in the air. The equation is d=1/2at^2. Our answer was 24.8m which is equivalent to 81.4 ft.
- Potential Spring Energy- This is how much potential energy the spring has when it is stretched. THe equation is different than that of potential energy; it is 1/2kx^2. Where x is the distance that the rubber band is stretched. Our potential energy was 78.22J.
- Kinetic Energy- this tells you how much of the potential energy got converted to the movement of the object. Theoretically it should be the same, but that is not always true because a lot of energy is lost to heat. We had 3.1J of kinetic energy.
- The percent of energy transferred was about 4%.
Dimensions
- The height of the fulcrum from the ground is 31.5 cm.
- The longest point at any given time is exactly one meter.
- The dimensions of the base is 24.5cm by 19.5 cm.
- The total length of the arm is 63cm.
- The length of the load part of the arm is 42.5 (that is the side with the clay weight hanging off of it).
- The length of effort part of the arm is 21cm.The longest point at any given time is exactly one meter.
- The length of the load part of the arm is 42.5 (that is the side with the clay weight hanging off of it).
Reflection
I had a lot of fun in this project and I learned a lot. One of my strengths in this project was that I felt more comfortable and confident when stating my ideas. That boosted my overall confidence and made me more social with my teammates and my friends. This will help me in future projects because I hopefully will not be as shy when sharing my ideas and thoughts. Also I wasn't the "leader" of the project, but we all were. In that perspective we were able to get more accomplished because we were able to ask our question to any team member since we were all on the same page.
One of my downfalls in this project was that I occasionally interrupted my teammates. Even though they were not bother by it, I personally felt rude by doing it.I can add my comment to their idea went they are done talking because I do not want them to feel that their idea or opinion is not worthy enough. Next time I can say what I want to say when they are done explaining their idea as to not be rude to them.
One of my downfalls in this project was that I occasionally interrupted my teammates. Even though they were not bother by it, I personally felt rude by doing it.I can add my comment to their idea went they are done talking because I do not want them to feel that their idea or opinion is not worthy enough. Next time I can say what I want to say when they are done explaining their idea as to not be rude to them.