Fire Away!
Our project was to create a trebuchet, or catapult to launch a projectile as far as possible. Our trebuchet had to be smaller than a cubic meter and launch as far as possible. Our projectile went 54 meters which was the farthest out of all the groups and was very powerful due to the 12 rubber bands we used to launch it.
Proof of Efficacy Document
Our trebuchet was 57 cm high and used 6 sets of 2 rubber bands to launch a 10 gram clay ball as far as possible. Our arm was 24 cm long which allowed for a further launch. We used 2 2x4s to support the axle which was a ½ inch in diameter.
After building our prototype, we made modifications to improve the quality of our trebuchet. Our modifications were:
For our experiment, we studied the release nail in a trebuchet and see how it affected the projectiles release and the overall result of the launch. For a trebuchet, the ideal angle of the release nail is a forward facing 40-90 degrees. Nail length was found to be irrelevant. We found that 40 degrees was too acute and gave a too shallow trajectory and was found to be incompetent. We then tested 90 degrees where the nail was straight and the ball flew too vertical and the ball didn’t travel far enough. We compromised between them and used 65 degrees which had also proven to be better than all other angles we had tested.
Our trebuchet launched our ball 54 meters which was the furthest out of all the groups in our class.
Our trebuchet was 57 cm high and used 6 sets of 2 rubber bands to launch a 10 gram clay ball as far as possible. Our arm was 24 cm long which allowed for a further launch. We used 2 2x4s to support the axle which was a ½ inch in diameter.
After building our prototype, we made modifications to improve the quality of our trebuchet. Our modifications were:
- We changed the mass of our clay ball to 10 grams so the ball wouldn’t fall so fast
- We lengthened our launch string which adds mechanical advantage to the trebuchet by adding distance to the lever and distance to the ball
- We changed the angle of the release nail to find the ideal position for a perfect launch
- We increased the number of rubber bands we used vastly and our final product uses 12 in 6 sets of 2
- At first we released the arm from 90 degrees and the ball flew backwards or straight up but we began releasing from a lesser angle making the ball go forward but losing energy
- We added 2 nails to the short end of the arm to help attach rubber bands and make firing more consistent
- We didn’t connect any rubber bands to the nail in the center of the trebuchet so the ball’s energy would be more forward
- We put the arm in the center of the axle so there would be less sideways energy and more of the energy would go forward.
For our experiment, we studied the release nail in a trebuchet and see how it affected the projectiles release and the overall result of the launch. For a trebuchet, the ideal angle of the release nail is a forward facing 40-90 degrees. Nail length was found to be irrelevant. We found that 40 degrees was too acute and gave a too shallow trajectory and was found to be incompetent. We then tested 90 degrees where the nail was straight and the ball flew too vertical and the ball didn’t travel far enough. We compromised between them and used 65 degrees which had also proven to be better than all other angles we had tested.
- The mass of our projectile was 10 grams which is a perfect mass for maximum distance
- Our projectile traveled 54 meters horizontally which was further than most other trebuchets that were tested
- Our projectile was airborne for 3.7 seconds mand was rising for 1.85 seconds and falling for 1.85 seconds and landed after 3.7 seconds
- The projectile reached a height of 16.6 meters which was the peak of its flight meaning that most of the energy went forwards rather than up
- The ball traveled horizontally at 14.6 meters per second. Which is the speed of the ball relative to the ground
- The ball traveled 18.13 meters per second vertically or up
- The total velocity is 23.28 meters per second. You find this by adding the vertical velocity squared and the horizontal velocity squared and finding the square root of the sum
- The ball is released at a 65 degree angle
- The spring constant is 87.6 N/m which is the amount of energy in he spring
- The spring has an initial potential energy of 90.48 joules which will be transferred into launching the ball
- Since the ball is so light and most of the energy is used to swing the arms, the ball only carries 2.71 joules of kinetic energy
- Only 3% of the total energy is transferred into the ball’s motion
Our trebuchet launched our ball 54 meters which was the furthest out of all the groups in our class.
Physics Concepts
Spring Constant (k)-stiffness of a spring or tendency of a spring to go back to its original form
Spring concept=Force/distance (N/m)
Potential Energy of the Spring (PEspring)-energy stored by expanding stretching or compressing an elastic object.
PEspring=1/2(spring constant)(distance spring is compressed or expanded)^2 (J)
Velocity (v)-rate of covered distance in a direction
Velocity=change in distance/change in time (meters/second)
Acceleration (a)-rate of change of velocity
Acceleration= change in velocity/change in time (meters/second squared)
Spring Constant (k)-stiffness of a spring or tendency of a spring to go back to its original form
Spring concept=Force/distance (N/m)
Potential Energy of the Spring (PEspring)-energy stored by expanding stretching or compressing an elastic object.
PEspring=1/2(spring constant)(distance spring is compressed or expanded)^2 (J)
Velocity (v)-rate of covered distance in a direction
Velocity=change in distance/change in time (meters/second)
Acceleration (a)-rate of change of velocity
Acceleration= change in velocity/change in time (meters/second squared)
Reflection
My group did well as a team and problem solved and focused well. Our group was able to launch our projectile further than any other group. I feel that my group did well designing and building our trebuchet. If I was to do this project again I would like to see if I could design a new model and see if we could beat our record. My group used rubber bands to provide the energy to launch the clay ball. I think this project was fun and educational because I learned about the spring constant and launching items.
My group did well as a team and problem solved and focused well. Our group was able to launch our projectile further than any other group. I feel that my group did well designing and building our trebuchet. If I was to do this project again I would like to see if I could design a new model and see if we could beat our record. My group used rubber bands to provide the energy to launch the clay ball. I think this project was fun and educational because I learned about the spring constant and launching items.