Fire Away!

Our Task

For this project I was put in a group with Megan Lobl and Nicholas Di Pasqua. The assignment was to create a launching device sending a projectile as far as possible. It needed to be portable, reusable, have a stable base, and no dimension of the device could be larger than 1 meter. After we made our first design, 4-5 modifications had to be made to improve the machine. My group helped each other with our designs and analysis of the machines.

Description

I built a trebuchet which used a series of items found from around my house. I took an extra kitchen stool, an old kids lacrosse stick, rubber bands, and duct tape. I layed the lacrosse stick across my chair to make a strong arm and using the chair as a stable base for my machine. I then duct taped it in place on the bottom of the stick creating an axle or a secure pivot point for the stick. Then I looped together 6 rubber bands and attached the stick and the chair together, stretching out the bands, creating a high source of energy

Modifications

The goal of the project was to send a projectile as far as possible. Therefore, we had to modify the machine to make it the most productive. The modifications I made to my machine included:

  1. More parallel links of rubber bands--more PE to be converted into KE which creates a higher velocity, allowing the projectile to travel further.

  2. Different arm ratio (higher arm to load)--when the ratio of load length to effort length is high, the load length is large while the effort length is low. Knowing this, applying a large Force we have a small distance, a small Force and a large distance, which results in the projectile flying further.

  3. More stretch and tension in the rubber band links--The higher the tension, the higher the force is, creating a larger MA, allowing the projectile to travel further.

  4. A lighter projectile--This makes the KE to be more consistent, making the velocity higher, allowing the projectile to travel further.

These modifications allowed my projectile to travel much further.

Variable: Number of rubber band links.

Claim: The less rubber bands linked together, the farther the projectile goes.

Claim, Evidence, and Reasoning

My group participants were Megan Lobl and Nicholas Di Pasqua. Our assignment was to create a single variable experiment to see how it impacted the distance the projectile traveled. As you can see to the left, we found that the less rubber bands linked together, the farther the projectile travelled. With more rubber bands in parallel, the projectile also travels a further distance.

Technical Specifications

Because we are learning distantly this year, everyone’s machines look a little bit different. Here are the details about mine.


Mass of Projectile: The ping pong ball I used was 0.0027kg.

Horizontal Distance: The average distance my projectile traveled was 8.86m.

Time in Air: The average time my projectile was in the air was 1.36s.

Vertical Distance: To find the projectile’s vertical distance I used the equation dv=½(a)(t)^2. I plugged in the numbers for acceleration(9.8m/s) and for the time of the fall(0.68s) to get a vertical distance of 3.33m.

Horizontal Velocity: To find the horizontal velocity I used the equation V=distance/time. Once I plugged the numbers in, I got a horizontal velocity of 6.5m/s.

Vertical Velocity: To find the vertical velocity I used the equation V=acceleration(time). I plugged in the numbers to get a vertical velocity of 13.32m/s.

Total Velocity: I found the vertical velocity by using the Pythagorean Theorem(a^2+b^2=c^2). The a and b values are the horizontal and vertical velocities (found above). Once plugged in, the total velocity was 14.8m/s.

Release Angle: I found the release angle of the projectile by using the trig function tan(x). The opposite side was the vertical velocity(13.32m/s) and the adjacent side was the horizontal velocity(6.5m/s). Once I calculated the problem, the release angle came out to be 26 degrees.

Spring Constant: To find the spring constant, I divided the Force of the rubber band(5N) by the distance it covered(0.1232m). These values were found by using a spring scale to measure the distance a rubber band covered when stretched with a force of 5N. I then multiplied that number by 4 because I used 4 rubber bands in my machine. My final spring constant was 162.4N/m.

Spring PE: The Spring PE was found with the equation PEspring=½(spring constant)(distance spring was stretched)^2. The spring constant was found above(162.4N/m) and the distance the spring was stretched was 20.32cm or 0.203m. When multiplied together, the spring PE was 16.48J.

KE: To find the KE, I used the formula KE=½(mass)(velocity)^2. The mass was 0.027kg and the velocity was the total velocity found above(14.8m/s). When all combined, the KE was 2.95J.

Percent Converted: When finding the amount of energy that was converted, I divided the KE(2.95J) by the PE(16.48J) which are both found above. After calculating, the total percent converted was 0.179 or 17.9%.

Main Selling Points

My trebuchet is one of the best because it is dependable, transportable, reusable, and handcrafted. The arm is made from a strong plastic so it won't break. The machine is easy to move around and can be easily taken apart and put back together if necessary. Lots of research and trials were done to make this design produce the best results. Ideas like a strong base, good load to effort ratio, less rubber bands, and a lighter projectile were all compiled into one machine. Lastly, my trebuchet makes a projectile fly the perfect amount. Just over 8.5 meters is the perfect distance because it’s not too small but not too long. That is why my trebuchet is the best!

Proof of Efficacy Document

Although everything on the document was listed above, embedded below is my official Proof of Efficacy Document.

Logan MacDonald - Proof of Efficacy Document for Trebuchet

Reflection

Overall I think this was one of the most challenging projects to complete distantly. Although I had a successful trebuchet, I came across problems that required lots of communication to the point where I felt like a burden to my team. However, I think my group did well getting our project done and I am glad I had people to work with.

With this being a more independent project, I feel I was very self-sufficient and worked through my problems. I got my work done by all the deadlines and I felt very organized. As I said before, this project required lots of communication to where I felt like a burden. This may have been because of the way the project was introduced or just our group dynamic, but for the next project I would like to encourage my group mates to share about their projects. I want to help people the way they help me but I can not do that if nobody talks in the group. I am excited for the next project so I can help others to learn and do their best.