Here is the video of our trebuchet working.
Proof of Efficacy
Description-A trebuchet (French trébuchet) is a type of siege engine which uses a swinging arm to throw a projectile at the enemy. The traction trebuchet first appeared in Ancient China during the 4th century BC as a siege weapon. We are using it as a way to measure and learn about spring constant. In class my group made a trebuchet that was able to launch a clay projectile 37m.
8 modifications-
- String length-we increased the string length so the projectile was able to leave at a 45 angle. If the angle is too high it goes up or down not out.
- Mass of projectile-the mass of our projectile was increased with the intent to further distance. If the projectile was too big then the air resistance would slow it down. If it was too small it wouldn't have the mass to launch far.
- Base structure-we added a second base because our original design when fired would fall over. The second base added more support since it was larger.
- Arm ratio-the arm ratio is important to determine the angle of release. The angle of release is the main factor
- Release nail angel-we worked on the nail angle for a while so we made a lot of adjustments. The finishing nail held the string attached to the projectile.
- Added spring-we added a spring to hopefully increase the distance.our original distance average was 5m-10m. Our final distances went 30m-35m.
- Number of rubber bands-we added rubber bands to increase the spring constant to further the distance.
- Types of rubber bands-we used rubber bands that were linked in pairs because our original rubber band snapped.
Clear paragraph-Catapult
When firing your catapult with a projectile attached to a string linked on a nail you want the nail facing forward at a 60° angle. We built a trebuchet with two legs one axle one base and an arm attached to the axle. We used rubber bands as our source for energy and the effort was us setting the catapult. Our projectile was a piece of clay. Our goal was to fire the projectile as far as possible. With the nail holding the string a 60° angle worked best. We did three trials with the angles of 90°, 45°, 135°, 70°, and 60°. The 60° nail allowed the projectile to travel 10m. 70° went 9m. 135° angle shot the projectile 4.3m. 45° angle of the nail released the projectile to travel 4m. Finally the 90° shot the shortest distance at 3.3m. The evidence can conclude that with a trebuchet shaped like ours a 60° works best for longer ranges. The angle of the nail affected where the projectile would release from the catapult.The 60° angle allowed the projectile to release at a 45° angle increasing the distance.
-We drilled the arms into the first base then drilled the first base through the second base. We stuck the dowel through to drilled holes that were in the arm. We stuck the arm through the dowel then added rubber bands and springs.
- a. Mass of your projectile-(0.011kg) About three teaspoons of sugar.
- b. Horizontal Distance-(36m) Almost as tall as a four story building.
- c. Time in air-(2.8s) We measured this with a stopwatch recording.
- d. Vertical Distance (d = 1/2 a t^2) where t is the time falling.-(9.6m) The height that the clay went was almost 30ft high.
- e. Horizontal velocity (v = d/t)-(3.42m/s) 7mph.
- f. Vertical velocity (v=at)-(27.4m/s) About 60mph
- g. Total velocity (a^2 + b^2 = c^2)-(27.4m/s) About 60mph.
- h. Spring constant (k=F/d)-(525J) The force divided by the distance.
- i. Initial Spring Potential Energy (PE spring = 1/2 k x^2)- Rubber Bands (20.58J) Spring PE(6.72J) You take the spring constant and divide it by two then you take the change in spring length multiply it by itself
- j. Kinetic energy of the ball (KE = 1/2 m v^2)-(4.129J) You take half the mass and multiply it by
- k. Percent energy converted (KE/PE)-(15.07%) I divided the kinetic by the potential energy.
Parts
Base1-(L57cm)(H2cm)(W32cm)
Base2-(L23cm)(H2cm)(W23cm)
Leg1-(L2cm)(H30cm)(W7cm)
Leg2-(L2cm)(H30cm)(W6cm)
Arm-(L4cm)(H57cm)(W4cm)
Dowel-(L16cm)(H1.5cm)(W1.5cm)
Main selling points-out trebuchet wasn’t the farthest firing one but it had a decent distance. The distance of the projectile matters so if you have a far away target then you are more likely to hit them.
Another thing we added was a spring. The spring shows originality because not many groups used a spring. Our catapult also can be adjusted easily to hit a target that is on a higher ledge.
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Evidence of Work-Our goal was to make a catapult that could launch a projectile a great distance. We learned about spring constant through this project. To complete the project we needed to make a proof of efficacy document that had information about our catapult and changes we made to the catapult.we started by getting a base we thought would be a good size but later realized was to large and was unnecessary at the time. Our next step was getting the arm that would hold the projectile, and the legs that would be screwed to the base. Once we got the catapult completed it only fired 0m-10m so we obviously had to make adjustments so it could compete with others. Finally we made 8 distinct modifications listed in the proof of efficacy.
Content:
a. Distance vs. time-D/T. We measured the speed it traveled at each meter.
b. velocity-The rate of covered distance in a direction. D/T
c. Spring Potential Energy-Stiffness of a spring the tendency of a spring to go back to it's original form
d. Gravitational Potential Energy-Energy an object has due to its position has due to its position at a height or in a gravitational field
e. Kinetic Energy-Energy due to motion
f .Thermal Energy (and how it relates to the conservation of energy)
g. Friction-push or pull on an object Can't be calculated.
Reflection for Trebuchet and Hybrid Car Projects
In the trebuchet project I was really good with communicating my ideas and problem solving. If we couldn't find a part like rubber bands that would be a problem. So to solve it I would go get the item. Finally when designing our Trebuchet I shared the ideas I had or options we could all collaborate on and choose the best outcome for our catapult. I suggested we should use a larger base so when firing the momentum wouldn't knock it over. In the Hybrid Vehicle Project I feel I demonstrated a good job in collaboration and time management. In the beginning of the project we started with several ideas for a vehicle that would work. I believe I contributed many ideas towards my groups design. When we finally settled on a design we finished making the vehicle in one build day so we were very productive day and had lots of time to spare.
Something I hope to improve on for the Trebuchet project is time management, and planning. The first day we started building we had little research on how trebuchets worked and how to make an effective one. I didn't really know what i was doing and in the future I would rather have done more planning so i would know how to create a great catapult. I would also want to work on my time management because I barely had enough time to finish the proof of efficacy document so in the future I will space out my time instead of procrastinating. For the Hybrid Car Project I think I should work on planning and presenting because i had a difficult time with both of these. When presenting I should enunciate more clearly and not rush through the information missing big parts of it. I don't think i really struggled in planning but I would like to do more of it with projects. I will research the topic in further depth and make a blueprint to scale so I have a better understanding of how we should solve the task.