Proof of Work / Content
Proof of Efficacy Document
For this project, had to build a trebuchet that had no dimensions larger than 1 meter. The trebuchet had to launch its projectile, a clay ball, at least 5 meters. We had any materials and tools in the San Marin maker space to build our trebuchet, as well as three days time.
Modifications:
The less space between the arm and the legs of the trebuchet, the further the projectile will launch. My group designed a trebuchet which can launch clay ball about the size of a piece of gravel. In our first launch tests, we discovered that the arm of our trebuchet (the long piece of wood that rotates upon launch) was unstable and not converting enough potential energy into kinetic energy where we wanted. We then conducted an experiment to determine how to best stabilize the arm. We measured the gap between the axle of the trebuchet and the arm and found it was 3.5 cm total. This is about 1.75 cm on each side of the axle. We cut a pvc pipe into two 1.5 cm sections to use as spacers for between the axle and arm on either side of the arm. This made the gap 0.25 cm on each side of the arm. When we had fired the trebuchet without the spacers, the average distance traveled by the projectile was 11.8 meters. With the spacers in, the average launch distance was 14 meters. This can explained because our machine has a set amount of potential energy which will be converted into kinetic energy upon firing. The spacers guide the arm so that more of the potential energy converts into kinetic energy in the direction that we want, which is forward.
Design
Our base is a 22.5 inch 2 x 6 piece of wood. Our arms are both 13 inch tall 2 x 4s which are screwed into the base about 3 inches apart. Our axle is a foot long, ⅔ inch in diameter, hollow metal rod. Our arm is a long, thin piece of wood which has the firing nail sticking out about one inch. The projectile that we fired is a clay ball wrapped in duct tape to prevent the string from ripping out upon firing. The string is about 8 inches long when in place to launch. We got our spring potential energy from 12 size 64 rubber bands in links of two. Two links were attatched to the right side of the base, two to the left, and two to the front. The rubber bands hung on to the arm by a bolt which was driven through the arm about half an inch from the edge.
During the alternative energy vehicle project, the goal was to design and build a vehicle of some sort that could carry a mass as close to 5 meters as possible. This mass was not just any mass, however, it represented two living passengers. This meant that the passengers would have to have a safe journey, and that the vehicle would have to be convenient for them. No Super high climbs to get to the top of a ramp. No dragging the passengers across the floor. We would be downgraded if the passengers, which turned out to be two rolls of pennies, had any rips in their "skin" by the end of the project. The vehicle could not use battery power unless the batteries got their energy from the sun. At first, my group thought we would go down the solar power path, but after we built our first prototype, we realized that the solar panel that we had was too weak to move our car. From there, we chose to use gravitational potential energy. Obviously, it was time to make a zip line. However, we needed a way to lift the passengers up to the top of the zip line without human help. We came up with the idea to use a counterweight to pull the pennies up to the top using a pulley system. From there, the pennies travel exactly 5 meters down the zip line to their destination.
Proof of Work / Content
Proof of Efficacy Document
For this project, had to build a trebuchet that had no dimensions larger than 1 meter. The trebuchet had to launch its projectile, a clay ball, at least 5 meters. We had any materials and tools in the San Marin maker space to build our trebuchet, as well as three days time.
Modifications:
- 60° Nail Angle - When another group did an experiment, they found that the nail angle for farthest was 65° and 85°, as opposed to straight with the arm. However, our machine was a little different. My group’s trebuchet launched the farthest when the nail at the end of the arm was at 60°. This is because the projectile launches at 57°, which is the optimal firing angle for our machine.
- Spacers in Between Arm and Legs on Axle - The spacers reduce the arm’s wobble when launching. This make more of the machines potential energy convert into kinetic energy in the direction that we want it to, which is forward and up.
- Rubber Bands Instead of Weight - When we first built our trebuchet, we used a counterweight to pull down the arm instead of rubber bands. This method did not launch the projectile very far if at all. When we switched to rubber band power, we immediatly improved by twelve meters on our launch distance. This obvious difference is because with a weight, only gravity is acting on the arm, so there is not enough time for the arm’s velocity to build up. With rubber bands, there is not only the force of gravity, but the spring constant in the rubber bands. Ths causes a greater force and a farther launch.
- No Arm Stopper - On our modification day, we tried adding an arm stopper, and we found that our machine fired weaker and shorter. When we took it back off, our results immediatly improved. This is because a stopper prevents the arm from completing a full rotation, which makes the launch angle higher. This causes more of the machine’s energy to go up instead of forward, which is bad.
- 15 cm String - The longer the string that is attatched to the projectile, the faster the ball moves, therefore the farther the ball launches. This is because the arm will still move at the same rate, but the ball has a longer distance to cover because of its larger radius in relation to the axle. So, the ball travels a longer distance in the same amount of time, which means a higher velocity. However, if the string is too long, it causes too much friction with the ground and it slows the projectile down.
- Tape Around Projectile - The tape around the clay ball was a modification more for convenience, but it helped all the same. We made this modification because the string in the projectile kept ripping out due to the force of the trebuchet launching. The tape around the clay was harder for the string to rip through, so it stopped, if not slowed down, the string from ripping out of the clay ball.
- 17 Gram Projectile - On the day when all of the groups made and explained modifications to their trebuchets, two teams experimented with the mass of the ball. One group found the most success with a 10 gram ball, and the other group’s winner was 22.5 grams. When we made changes to our projectile, we found that a middleground ball, at 17 grams worked the best. If the ball is too large and heavy, it will have too much air friction and mass to launch very far. If it is too light, it will not have enough momentum to go far.
- Size 64 Rubber Bands - We used size 64 rubber bands because they were in the largest supply, and they launched the projectile the farthest. If the rubber bands are too short and thick, they do not stretch far enough to get a good force pulling down. If they are long and thin, they are not strong or durable. Size 64 rubber bands are thick enough to give a strong force and be durable, and long enough to pull over a long distance. This makes them perfect for launching our trebuchet.
The less space between the arm and the legs of the trebuchet, the further the projectile will launch. My group designed a trebuchet which can launch clay ball about the size of a piece of gravel. In our first launch tests, we discovered that the arm of our trebuchet (the long piece of wood that rotates upon launch) was unstable and not converting enough potential energy into kinetic energy where we wanted. We then conducted an experiment to determine how to best stabilize the arm. We measured the gap between the axle of the trebuchet and the arm and found it was 3.5 cm total. This is about 1.75 cm on each side of the axle. We cut a pvc pipe into two 1.5 cm sections to use as spacers for between the axle and arm on either side of the arm. This made the gap 0.25 cm on each side of the arm. When we had fired the trebuchet without the spacers, the average distance traveled by the projectile was 11.8 meters. With the spacers in, the average launch distance was 14 meters. This can explained because our machine has a set amount of potential energy which will be converted into kinetic energy upon firing. The spacers guide the arm so that more of the potential energy converts into kinetic energy in the direction that we want, which is forward.
Design
Our base is a 22.5 inch 2 x 6 piece of wood. Our arms are both 13 inch tall 2 x 4s which are screwed into the base about 3 inches apart. Our axle is a foot long, ⅔ inch in diameter, hollow metal rod. Our arm is a long, thin piece of wood which has the firing nail sticking out about one inch. The projectile that we fired is a clay ball wrapped in duct tape to prevent the string from ripping out upon firing. The string is about 8 inches long when in place to launch. We got our spring potential energy from 12 size 64 rubber bands in links of two. Two links were attatched to the right side of the base, two to the left, and two to the front. The rubber bands hung on to the arm by a bolt which was driven through the arm about half an inch from the edge.
- Base
- 57cm x 13.5cm x 4cm
- Arm
- 79.5cm x 4cm x 2cm
- Axle from base height = 30.5cm
- Axle diameter = 1.5cm
- Hollow metal
- Legs
- 33cm* x 4 cm x 9cm
- Angle of nail = 60° forward to where ball is launched
- MA of arm = 2.8
- Gap between arm and legs on axle = 0.25cm on either side due to spacers
- Projectile string = 15cm
- Mass of Projectile = 0.017 kg
- This is the weight of our clay ball that was fired
- Horizontal Distance = 38 meters
- The projectile landed 38 meters away from where it was fired from
- Time in Air = 1.725 seconds
- The projectile was in the air for 1.725 seconds after it was fired
- Vertical Distance = 14.58 meters
- The projectile went 14.38 meters straight into the air
- Horizontal Velocity = 22.03 m/s
- The projectile moved at a speed of about 22 meters every second sideways
- Vertical Velocity = 16.9 m/s
- When the projectile fell from the air after reaching its highest point, it fell at a speed of 16.9 meters every second
- Total Velocity = 27.77 m/s
- The ball was moving at that speed through the air
- Angle of Release = 60 degrees
- The trebuchet launches the ball at a 60° angle
- Spring Constant = 420 N/m
- Our rubber bands can apply 420 Newtons of force per meter. A pogo stick can apply up to 15,000 Newtons per meter.
- Potential Energy Spring = 22.869 J
- Our catapult stores about 23 Joules of energy when fully cocked back and ready to fire
- Kinetic Energy of Ball = 6.55 J
- When flying through the air at maximum speed, our projectile has about six and a half Joules of kinetic energy
- 29% of the original potential spring energy is converted into kinetic enrgy for the projectile
- Very efficient - Our trebuchet converts a shocking 29% of its potential energy into kinetic energy in the ball, which is great considering that the rubber bands have to pull the arm up as well.
- Far launch - 38 meters horizantally was the farthest our machine launched, putting it at the top of the 3 - 4° class.
- Cinematic launch - When it fires, our trebuchet puts the ball at a 60° angle, giving it a long, high trajectory. Seeing the ball fly so high and far reminds you of the good old fashion medieval trebuchets.
- Less rubber bands - Some other machines used ridiculous amounts of rubber bands and still did not launch as far as ours, which only used six.
- Easy to load - My teammate James had the idea to put in a crossbar that is braced on two nails that prevents the machine from misfiring when loading it. This one of a kind modification makes our trebuchet safer and more convenient than others.
During the alternative energy vehicle project, the goal was to design and build a vehicle of some sort that could carry a mass as close to 5 meters as possible. This mass was not just any mass, however, it represented two living passengers. This meant that the passengers would have to have a safe journey, and that the vehicle would have to be convenient for them. No Super high climbs to get to the top of a ramp. No dragging the passengers across the floor. We would be downgraded if the passengers, which turned out to be two rolls of pennies, had any rips in their "skin" by the end of the project. The vehicle could not use battery power unless the batteries got their energy from the sun. At first, my group thought we would go down the solar power path, but after we built our first prototype, we realized that the solar panel that we had was too weak to move our car. From there, we chose to use gravitational potential energy. Obviously, it was time to make a zip line. However, we needed a way to lift the passengers up to the top of the zip line without human help. We came up with the idea to use a counterweight to pull the pennies up to the top using a pulley system. From there, the pennies travel exactly 5 meters down the zip line to their destination.
Content - Continued
Velocity - Change in Distance/Change in Time m/s
Velocity describes the speed of an object in a certain direction. Our zip line's average velocity is 4.92 meters per second as it travels down the slope.
Gravitational Potential Energy - Mass x Acceleration due to Gravity x Height J
Gravitational potential energy describes an objects energy in relation to the ground. Our passengers have 3.27 joules of gravitational potential energy at the top of the zip line.
Kinetic Energy - 1/2 Mass x Velocity^2
An object has kinetic energy when it is in motion. Our zip line's maximum kinetic energy is 1.92 joules.
Thermal Energy - Total Energy -Kinetic Energy -Potential Energy J
Thermal energy is energy lost to friction within the system. All potential energy not converted to kinetic is converted to thermal energy.
Velocity - Change in Distance/Change in Time m/s
Velocity describes the speed of an object in a certain direction. Our zip line's average velocity is 4.92 meters per second as it travels down the slope.
Gravitational Potential Energy - Mass x Acceleration due to Gravity x Height J
Gravitational potential energy describes an objects energy in relation to the ground. Our passengers have 3.27 joules of gravitational potential energy at the top of the zip line.
Kinetic Energy - 1/2 Mass x Velocity^2
An object has kinetic energy when it is in motion. Our zip line's maximum kinetic energy is 1.92 joules.
Thermal Energy - Total Energy -Kinetic Energy -Potential Energy J
Thermal energy is energy lost to friction within the system. All potential energy not converted to kinetic is converted to thermal energy.
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Total Energy - Kinetic Energy + Potential Energy + Thermal Energy J
Total energy is all of the energy within the system you are observing. Our zip line's total energy is 3.27 joules
Friction - A force opposing the direction of motion due to roughness at the molecular level.
Friction causes loss of potential energy to thermal energy. Without friction, we would not be able to walk.
Reflection
During our Alternative Energy Vehicle and Fire Away! projects, I felt that I did very well as an all around teammate. I believe that I collaborated and solved problems exceptionally. I talked with my teammates and made sure that we all were on the same page. When we were working on our alternative energy vehicle, I made sure to keep our group informed and included. During the building of our trebuchet, we started off with using weights as the source of potential energy, but that was not working. I suggested that we switched to rubber band power, which ended up working very well. This was good problem solving.
Of course, nobody is perfect. Although I consider myself a good leader, I believe that I could have done better during these two projects as a leader. My teammate James seemed like he had too much of a burden on his shoulders and I wish that I had lightened his load a little. For example, when James was doing the calculations, I could have helped and done half of them or something. I guess I just got a little unfocused, but I will refocus going forward and not let my teammates down. My work ethic needs some work as well. I would like to be able to sit down and finish something, but I get distracted too easily. In the maker space, when we were working on our first prototype, I took much longer than needed to build the car's frame. Ikept getting distracted and experimenting with the solar panel. This was a waste of time that our group got through, but I need to stop doing things like that in the future.