The Project
The goal of this project was to create a “projecting device that will stay in one place and be reusable regardless of how many times you use it.” We were constrained to use a base that could be placed upon the ground, two legs holding up an axle, and a lever arm with a load and effort end. It would also have to be portable by one person and fit in a 1 meter cube at all times. The projecting device could not be aided in the firing of the projectile. The general purpose of these restraints were to limit us to use a form of a catapult or trebuchet. Springs, rubber bands, counterweights, and mousetraps were all being considered as possible mechanisms for our machine.
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Variables
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Numbers
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My Thoughts
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Proof Of Efficay Document
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Several variables were present in our catapult. A comprehensive study was launched, encompassing the areas of:
- Axle Height
- Input Energy
- Release Nail Angle
- Stopping Mechanism
- Load to Effort Ratio
- Projectile
- String Length on Projectile
- Arm Length
Axle Height
Through experimentation, we have established that the optimal position for a catapult axel is 10.5 inches, or as high as possible. We found this by running a sequence of twelve tests. We positioned our catapult with the same load and string, as well as a standard number of rubber bands. We fired our catapult at varying heights; three times at each height. We tested four positions: 8.5, 9.5, 10.5, and 11.5 inches. We found that the average distance traveled by the projectile, in meters, were 14.3, 14, 19.8, and 13.7 respectively. This shows the optimal height is 10.5 inches, and a higher axel generally gives more distance. We believe the reason why a higher axel gives a farther distance is that the higher position gives a higher spring tension, therefore giving more energy. In addition, this also gives a longer amount of time for the spring to act upon the throwing arm. This, in addition to the same amount of force, gives more distance. The reason that the 10.5 inch mark gave us our optimal distance is due to the release angle of the projectile. A higher position interfered with the release angle, as the throwing arm could not be stopped by the base of the catapult, therefore releasing the projectile too late to achieve the optimal angle. Therefore, it is reasoned that for our catapult and ones like it, a 10.5 inch axle height is optimal, whereas other catapults with other methods for achieving the optimal angle of release should aspire to have their axel as high as space and material constraints allow.
Input Energy
Thicker and more rubber bands produces more distance. This is because the input potential energy is compounded with the addition of more rubber bands. (i.e. One rubber band has (for example) a Joule of energy, so two rubber bands have a total of two Joules of potential energy) As a result, we used eight rubber bands.
Release Nail Angle
The angle that the release snail should be at is 10 degrees “backwards”. This means that the nail should be rotated 10 degrees counter-clockwise when the firing arm is in firing position parallel to the base. The reason for this is to enable the projection of the projectile to be closer to the optimal angle. The reason for not bending the nail further, is that the projectile would slip off the nail before firing. Without bending the nail, the projectile would be flung off the nail too late, resulting in it being hurled at the ground
Stopping Mechanism
A stopping device has no practical use on our catapult. This was found to be the case because it was found that the best way to manage the release angle was to alter the nail. A a stopper prematurely stopped the projecting arm, not only reducing its force, put introduces the possibility of having the arm shatter upon contact with the stopper. In some cases, the stopper stopped the arm after the projectile was released, rendering it useless. Therefore, we did not have a stopper.
Load to Effort Ratio
A 1:1 arm ratio, for our purposes, was the best. In theory, a higher effort to load ratio (1:4) would be best. However, this would have to be used in conjunction with a light projecting arm, which was not used. Therefore, we had to balance a high mechanical advantage with the effort of raising a heavy arm. (A higher mechanical advantage produces more force, but also requires more force to raise the arm the greater distance. Therefore, an equilibrium must be reached with each individual throwing arm.)
Projectile
A 7g spherical projectile was found to have the best results. This is due to the fact that a larger projectile was affected to a high degree with inertia, and any smaller projectile was slowed by air resistance.
String Length on Projectile
A string with a total length of 40 cm was found to be the best for throwing the projectile. A longer string prevented the sphere from gaining much momentum, as the string was being pulled long before the projectile was. However, a short string prevented the projectile from swinging around in a satisfactory motion.
Arm Length
No arm length was found to be the best. One study found the optimal length to be 47.5 cm. However, under close scrutiny, it was revealed that different types of wood were used, therefore skewing the results.
Following will be the relevant technical information for our catapult under an average run.
Horizontal Distance:
23 Meters or 75.5 Feet
Time in Air:
0.85 Seconds
Vertical Distance:
3.5 Meters or 11.5 Feet
Horizontal Velocity:
27 Meters/Second or 88.5 Feet per Second or 60 Miles per Hour
Vertical Velocity:
3.5 Meters/Second or 11.5 Feet per Second or 26 Miles per Hour
Total Velocity:
27 Meters/Second or 88.5 Feet per Second or 60 Miles per Hour
Angle of Release:
7.4 Degrees
Spring Constant (K)
157.5 Newtons/Meter or 35.4 pounds of force to stretch one meter.
Potential Energy of the Spring:
36.2 Joules or the force required to lift 36 medium-sized tomatoes a meter above the ground.
Kinetic Energy of the Projectile:
2.5 Joules (2.5 tomatoes)
Percent of Energy Transferred:
7% (Not very efficient as catapults go)
This project was a comparatively short one, with the build time being only one week. Nevertheless, many things were learned by me in this short time span. This project, I thought, did an admirable job of teaching us about rotational inertia, rotational forces, spring constants, and spring potential energy, among other things. It also taught us concepts not usually found in a classroom setting, such as when to pull the plug on part of a project.
As a group, I felt that we were very organized and effecient. We had our catapult firing within the first couple days, and the quality of construction leaped over the bar set by my previous projects. I felt as this was a straightfoward project, there was not so much brainstorming that had to be done. This allowed us to focus our efforts into making a functioning machine. Also, I felt that I did a good job of getting my portion of the project done, but staying out of the way of others in my group.
However, there were a number of things that could have gone better. TThis group was a meshing together of many different areas of thought, and they did not react well with each other. Frankly, I felt that as a group, we needed to do a better job of splitting up the work and enabling members to activly contribute. On a personal scale, it was interesting to see how my hands-off approach interacted with the group members that I had not worked with. I think it fair to say that it did not work, and I will have to re-evaluate this approach in the future.
Overall, I think that this project was an interesting experimentation, and helped me a great deal in terms of furthering my education.
As a group, I felt that we were very organized and effecient. We had our catapult firing within the first couple days, and the quality of construction leaped over the bar set by my previous projects. I felt as this was a straightfoward project, there was not so much brainstorming that had to be done. This allowed us to focus our efforts into making a functioning machine. Also, I felt that I did a good job of getting my portion of the project done, but staying out of the way of others in my group.
However, there were a number of things that could have gone better. TThis group was a meshing together of many different areas of thought, and they did not react well with each other. Frankly, I felt that as a group, we needed to do a better job of splitting up the work and enabling members to activly contribute. On a personal scale, it was interesting to see how my hands-off approach interacted with the group members that I had not worked with. I think it fair to say that it did not work, and I will have to re-evaluate this approach in the future.
Overall, I think that this project was an interesting experimentation, and helped me a great deal in terms of furthering my education.
The goal of this project was to create a “projecting device that will stay in one place and be reusable regardless of how many times you use it.” We were constrained to use a base that could be placed upon the ground, two legs holding up an axle, and a lever arm with a load and effort end. It would also have to be portable by one person and fit in a 1 meter cube at all times. The projecting device could not be aided in the firing of the projectile. The general purpose of these restraints were to limit us to use a form of a catapult or trebuchet. Springs, rubber bands, counterweights, and mousetraps were all being considered as possible mechanisms for our machine.
Several variables were present in our catapult. A comprehensive study was launched, encompassing the areas of:
Following will be the relevant technical information for our catapult under an average run.
Horizontal Distance:
23 Meters or 75.5 Feet
Time in Air:
0.85 Seconds
Vertical Distance:
3.5 Meters or 11.5 Feet
Horizontal Velocity:
27 Meters/Second or 88.5 Feet per Second
Vertical Velocity:
3.5 Meters/Second or 11.5 Feet per Second
Total Velocity:
27 Meters/Second or 88.5 Feet per Second
Angle of Release:
7.4 Degrees
Spring Constant (K)
157.5 Newtons/Meter or 35.4 pounds of force to stretch one meter.
Potential Energy of the Spring:
36.2 Joules or the force required to lift 36 medium-sized tomatoes a meter above the ground.
Kinetic Energy of the Projectile:
2.5 Joules (2.5 tomatoes)
Percent of Energy Transferred:
7% (Not very efficient as catapults go)
Several variables were present in our catapult. A comprehensive study was launched, encompassing the areas of:
- Axle Height
- Input Energy
- Release Nail Angle
- Stopping Mechanism
- Load to Effort Ratio
- Projectile
- String Length on Projectile
- Arm Length
- Through experimentation, we have established that the optimal position for a catapult axel is 10.5 inches, or as high as possible. We found this by running a sequence of twelve tests. We positioned our catapult with the same load and string, as well as a standard number of rubber bands. We fired our catapult at varying heights; three times at each height. We tested four positions: 8.5, 9.5, 10.5, and 11.5 inches. We found that the average distance traveled by the projectile, in meters, were 14.3, 14, 19.8, and 13.7 respectively.
- Thicker and more rubber bands produces more distance. This is because the input potential energy is compounded with the addition of more rubber bands. (i.e. One rubber band has (for example) a Joule of energy, so two rubber bands have a total of two Joules of potential energy) As a result, we used eight rubber bands.
- The angle that the release snail should be at is 10 degrees “backwards”. This means that the nail should be rotated 10 degrees counter-clockwise when the firing arm is in firing position parallel to the base. The reason for this is to enable the projection of the projectile to be closer to the optimal angle. The reason for not bending the nail further, is that the projectile would slip off the nail before firing. Without bending the nail, the projectile would be flung off the nail too late, resulting in it being hurled at the ground
- A stopping device has no practical use on our catapult. This was found to be the case because it was found that the best way to manage the release angle was to alter the nail. A a stopper prematurely stopped the projecting arm, not only reducing its force, put introduces the possibility of having the arm shatter upon contact with the stopper. In some cases, the stopper stopped the arm after the projectile was released, rendering it useless. Therefore, we did not have a stopper.
- A 1:1 arm ratio, for our purposes, was the best. In theory, a higher effort to load ratio (1:4) would be best. However, this would have to be used in conjunction with a light projecting arm, which was not used. Therefore, we had to balance a high mechanical advantage with the effort of raising a heavy arm. (A higher mechanical advantage produces more force, but also requires more force to raise the arm the greater distance. Therefore, an equilibrium must be reached with each individual throwing arm.)
- A 7g spherical projectile was found to have the best results. This is due to the fact that a larger projectile was affected to a high degree with inertia, and any smaller projectile was slowed by air resistance.
- A string with a total length of 40 cm was found to be the best for throwing the projectile. A longer string prevented the sphere from gaining much momentum, as the string was being pulled long before the projectile was. However, a short string prevented the projectile from swinging around in a satisfactory motion.
- No arm length was found to be the best. One study found the optimal length to be 47.5 cm. However, under close scrutiny, it was revealed that different types of wood were used, therefore skewing the results.
Following will be the relevant technical information for our catapult under an average run.
Horizontal Distance:
23 Meters or 75.5 Feet
Time in Air:
0.85 Seconds
Vertical Distance:
3.5 Meters or 11.5 Feet
Horizontal Velocity:
27 Meters/Second or 88.5 Feet per Second
Vertical Velocity:
3.5 Meters/Second or 11.5 Feet per Second
Total Velocity:
27 Meters/Second or 88.5 Feet per Second
Angle of Release:
7.4 Degrees
Spring Constant (K)
157.5 Newtons/Meter or 35.4 pounds of force to stretch one meter.
Potential Energy of the Spring:
36.2 Joules or the force required to lift 36 medium-sized tomatoes a meter above the ground.
Kinetic Energy of the Projectile:
2.5 Joules (2.5 tomatoes)
Percent of Energy Transferred:
7% (Not very efficient as catapults go)