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Our Task
Our Task
Our task was to create a trebuchet or catapult that launched a projectile as far as possible. The catapult had to include a swinging lever, base, and axle.
The calculations
The calculations
a. Mass of your projectile: 40g -mass of a golf ball
b. Horizontal Distance: 32m -roughly the length of a bowling lane
c. Time in air: 0s
d. Vertical Distance: 0m
e. Horizontal velocity: 2.44m/s -about 5.5mph
f. Vertical velocity: 0m
g. Total velocity: 2.44m/s -about 5.5mph
h. Release angle: 0º
i. Spring constant: 350 N/m -spring constant of 5 rubber bands
j. Initial Spring Potential Energy: 2.1175J -potential amount of energy in machine
k. Kinetic energy of the ball: 0.488J -actual energy output on ball
l. Percent energy converted: 23% -most was lost in the swing of the stick
About Our Catapult
About Our Catapult
Instead of building a standard catapult or trebuchet, we decided to build an inverted catapult. We decided to turn our catapult upside down and have our catapult kick a ball. We used a golf ball as our projectile. The contraption had 5 rubber bands used as the springs. We pulled the lever about 180º back. This was to increase the force output from the lever.
The Iterations of Our Catapult
The Iterations of Our Catapult
Our catapult did not change that much. We had the idea of an inverted catapult from the beginning. The only things we changed were the pullback distance of the lever, the number of rubber bands, and our rubber band placement. We changed the pullback distance from about 90º to 180º This gave us maximum power. We changed from three rubber bands to five rubber bands. This was to increase the spring constant. Finally, we changed the rubber band placement starting from around the poles to be stretched from the base to the lever. This also increased the effectiveness of the rubber bands.
What We Did Well
What We Did Well
We were very creative. No one else in our class did anything like we did. We came up with a highly unique design. We also thought critically. When a problem came up we solved it quickly.
What We Could Improve On
What We Could Improve On
We could improve on collaboration. We did not work together very much on this project. We could also improve on communication. Some group members had trouble expressing their ideas.
The Iterations of Our Car
The Iterations of Our Car
The first iteration of our car was a complicated car with three axles, powered by rubber bands. A wooden block was to act as the body of the car. This ended up not working at all. We could not get the axles straight, so the car couldn't even roll well. We changed to body out for a cardboard box and connected rubber bands to the center of the axle. This got us much closer to the goal of 5 meters. We got closer to the 5 meters mark, but still very far away. We still needed to improve, so we hot glued CD's to the wheels to increase the distance. This got us to about 2 meters. Next, we hot glued the CD's on more accurately. We also changed out the body for a wooden block and tried using a ramp. The wooden block was too small so the wheels ran into each other repeatedly. Finally, we switched the body for the last time to a PVC pipe. We also used only two axles. We used the ramp and it worked perfectly!
Our Task
Our Task
Our task was to create a car that rolled as close to 5m as possible. The car also had to transport 2 rolls of pennies. We were not allowed to use batteries or any other chemical energy. We were also not allowed to use nuclear power.
About Our Car
About Our Car
Our car was made of PVC and toy car tires and axles. CD's acted as additive wheels. The car was powered by gravity. The ramp used gives a higher starting point. Our car went through a lot of iterations.
The Calculations
The Calculations
Gravitational PE: 0.5488J (at 0m w/ car on ramp)
Kinetic Energy: 0.19602J (at 1m)
Total Energy: 0.5488J
Thermal Energy: 0.35278J (at 1m)
Our wheel's rotational inertia is higher because there is more mass on the outside of the wheel compared to inside.
What We Did Well
What We Did Well
I believe that we were very good at critical thinking. When a problem arose we could think quickly and solve the solution. This is why we had so many iterations of our car. We also did well on collaboration. When we worked together we all made our parts functional.
What We Could Improve On
What We Could Improve On
I believe we could improve on creativity. Every design we had for our car was very straightforward and not very creative. We could also improve on communication. We had problems properly expressing ideas to each other.
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