Christina+FN-+Trebuchet+Project

=A Trebuchet  by Christina Fowlie-Neufeld =

**__The Physics of a Trebuchet:__**

A trebuchet uses many of the principles that we have discussed in class. The most important principle in building the trebuchet is the angle that an object is launched. The best angle for a projectile to travel from is 45°. The goal in building the trebuchet is to have the object be released from the machine at a point where it will fly at 45°. It is difficult to tell from video the exact angle that the object is released, but if the flight is timed and the distance measured the angle and velocity can be found using the kinematics equations.

Also an important factor is Newton's Second Law: unbalanced forces will cause acceleration. In this case the only force acting on the projectile is gravity which creates a downward acceleration, resulting in the parabolic shape of the trajectory.


 * __Materials__:**
 * 1 10x30 cm piece of light wood 3/4 inch thick
 * 4 28 cm long pieces of 3/4 inch square wood
 * a paint stir stick cut to 38cm long
 * 11cm long piece ¼ inch dowel
 * wood screws
 * glue
 * string
 * rectangular piece of leather
 * wire (I used an unbent paperclip)
 * tin can and lid
 * pebbles


 * __Procedure:__**

Preparing the uprights and braces:  Preparing the throwing arm: <span style="font-family: Georgia,serif;"> Preparing the counterweight(approx. 500g): <span style="font-family: Georgia,serif;"> Preparing the sling: <span style="font-family: Georgia,serif;"> Assembling the Trebuchet: <span style="font-family: Georgia,serif;">
 * 1) <span style="font-family: Georgia,serif;">On two of the 28cm long pieces saw both ends at 45 so that the long edge is still 28 cm.
 * 2) <span style="font-family: Georgia,serif;">In the other two 28cm pieces drill a hole 3cm from the top with a diameter of ¼ inch and a depth of .5cm.
 * 1) <span style="font-family: Georgia,serif;">Drill a small hole about 1cm from the end of the stick. This will be to hold the counter weight.
 * 2) <span style="font-family: Georgia,serif;">Drill a ¼ inch hole 8cm from that same end. This is where the arm will pivot.
 * 3) <span style="font-family: Georgia,serif;">Drill a hole 3cm from the opposite end. This is where the sling will be attached.
 * 4) <span style="font-family: Georgia,serif;">Saw a notch about 1cm long into the sling end of the arm.
 * 1) <span style="font-family: Georgia,serif;">Poke two holes, across from each other, into the side of the can about .5cm from the top
 * 2) <span style="font-family: Georgia,serif;">Fill a tin soup can with pebbles. Tape or glue the lid on so that the pebbles will not bounce out (the lid will have to go on after it is tied to the arm).
 * 3) <span style="font-family: Georgia,serif;">I covered the weight with paper to make it look nicer.
 * 1) <span style="font-family: Georgia,serif;">Cut a piece of leather 13cmx5cm
 * 2) <span style="font-family: Georgia,serif;">Fold it in half lengthwise with two long pieces of string coming from each corner. The length of the strings will be adjusted so that they are taut when the trebuchet is loaded
 * 3) <span style="font-family: Georgia,serif;">Hot glue the sides to make a 13cm long pouch
 * 1) <span style="font-family: Georgia,serif;">Screw one of the uprights to the base 21.5cm from the end of the base. Use a level to make sure that it is perpendicular (see 1.)
 * 2) <span style="font-family: Georgia,serif;">The brace should be screwed into the base about 20cm from where the upright is attached. The brace can be attached to the upright with glue or a screw ( I used both to ensure it was strongly attached).(see 1.)
 * 3) <span style="font-family: Georgia,serif;">Glue an 11cm piece of 1/4inch dowel into the drilled hole of the upright. (see 2.)
 * 4) <span style="font-family: Georgia,serif;">Fit the dowel through the ¼ inch hole in the arm.
 * 5) <span style="font-family: Georgia,serif;">Attach the second upright 21.5cm from the end with a screw.
 * 6) <span style="font-family: Georgia,serif;">Before the upright is screwed in tightly fit the other end of the dowel into the drilled hole and glue.
 * 7) <span style="font-family: Georgia,serif;">Attach the brace about 20cm from the upright and screw it into the base. (see 3.)
 * 8) <span style="font-family: Georgia,serif;">Glue and screw the brace to the upright.
 * 9) <span style="font-family: Georgia,serif;">Attach the counterweight to the end of the arm that is closer to the pivot by threading string through both holes in the can and the one in the arm.
 * 10) <span style="font-family: Georgia,serif;">To attach the pouch arrange it so that it opens away from the weight. Tie the string through the hole on the slotted end of the arm. The string should be a length of 20cm from the hole to the pouch. On the other end of the pouch tie the string at about 18cm from the pouch. Attach to this end a small wire ring 2cm in diameter. Make sure that the ring will slip easily in and out of the arm’s slot.
 * 11) <span style="font-family: Georgia,serif;">After the glue has set the trebuchet is ready to load. (see 4.)

__


 * Results:**__

<span style="font-family: Georgia,serif;"> I tested my trebuchet on a level floor that was clear of obstacles. To load it place the object in the pouch and pouch's ring into the arm's slot. Then pull the pouch and Christmas ball down and under toward the counterweight and back of the base. In a loaded position the pouch and object must be held in place. To launch simply let go of the pouch and the counterweight will drop.
 * = <span style="font-family: Georgia,serif;">Trial ||= <span style="font-family: Georgia,serif;">Mas (kg) ||= <span style="font-family: Georgia,serif;">Arm Length (m) ||= <span style="font-family: Georgia,serif;">Distance(m) ||= <span style="font-family: Georgia,serif;">P=d/ml ||
 * = <span style="font-family: Georgia,serif;">1 ||= <span style="font-family: Georgia,serif;">1.0 ||= <span style="font-family: Georgia,serif;">.76 ||= <span style="font-family: Georgia,serif;">4.50 ||= <span style="font-family: Georgia,serif;">5.92 ||
 * = <span style="font-family: Georgia,serif;">2 ||= <span style="font-family: Georgia,serif;">1.0 ||= <span style="font-family: Georgia,serif;">.76 ||= <span style="font-family: Georgia,serif;">3.90 ||||= <span style="font-family: Georgia,serif;">5.13 ||
 * = <span style="font-family: Georgia,serif;">3 ||= <span style="font-family: Georgia,serif;">1.0 ||= <span style="font-family: Georgia,serif;">.76 ||= <span style="font-family: Georgia,serif;">4.33 ||= <span style="font-family: Georgia,serif;">5.69 ||
 * = <span style="font-family: Georgia,serif;">4 ||= <span style="font-family: Georgia,serif;">1.0 ||= <span style="font-family: Georgia,serif;">.76 ||= <span style="font-family: Georgia,serif;">4.29 ||= <span style="font-family: Georgia,serif;">5.64 ||
 * = <span style="font-family: Georgia,serif;">5 ||= <span style="font-family: Georgia,serif;">1.0 ||= <span style="font-family: Georgia,serif;">.76 ||= <span style="font-family: Georgia,serif;">3.87 ||= <span style="font-family: Georgia,serif;">5.09 ||
 * = <span style="font-family: Georgia,serif;">6 ||= <span style="font-family: Georgia,serif;">1.0 ||= <span style="font-family: Georgia,serif;">.76 ||= <span style="font-family: Georgia,serif;">4.37 ||= <span style="font-family: Georgia,serif;">5.75 ||
 * = <span style="font-family: Georgia,serif;">7 ||= <span style="font-family: Georgia,serif;">1.0 ||= <span style="font-family: Georgia,serif;">.76 ||= <span style="font-family: Georgia,serif;">3.90 ||= <span style="font-family: Georgia,serif;">5.13 ||
 * = <span style="font-family: Georgia,serif;">8 ||= <span style="font-family: Georgia,serif;">1.0 ||= <span style="font-family: Georgia,serif;">.76 ||= <span style="font-family: Georgia,serif;">4.40 ||= <span style="font-family: Georgia,serif;">5.79 ||
 * = <span style="font-family: Georgia,serif;">Average ||= <span style="font-family: Georgia,serif;"> ||= <span style="font-family: Georgia,serif;"> ||= <span style="font-family: Georgia,serif;">4.195 ||= <span style="font-family: Georgia,serif;">5.52 ||


 * __Analysis:__**

The portion of the trebuchet that gave me the most trouble was the pouch and the release of the ornament. Originally the pouch was much deeper and the string was attached to the arm in only one place. I had the string strung through one hole in the arm and glued to both ends of the pouch. When I tested this I found that the ball stayed in the pouch for too long and didn't release until the arm was almost finished swinging. The farthest that I got it was less than half a meter. I found that the pouch didn't open wide enough to release the ball, so I decided to make it much shallower and I changed how the string was attached. I sawed a slot in the arm and put a ring on the end of the pouch string, but it was still permanently attached at one point. This allowed one end of the pouch string to detach from the arm during the launch which caused the pouch to go into a vertical position and fling the ball farther than before.

After I changed the pouch I still wasn't getting the results that I wanted. The farthest that it could throw was about 1.5m-2m. Since everything else was glued or screwed in already, the easiest action to take was to change the mass of the counterweight. I originally had used a round container filled with sand that had a mass of 250 g. I doubled the mass to 500 g by using a larger container (a tin can) and filling it with rocks. After this change my trebuchet was able to throw the ornament an average of about 4m consistently.

In many of the pictures that are I have shown small block of wood is seen screwed onto the back of the base. This was meant to be a trigger so that I wouldn't have to hold onto the pouch to keep it in a loaded position. This would have been very helpful, but I couldn't find anything that would easily slip through the trigger. I tried string but it got caught on rough wood and slowed down the arm. I also tried wire but didn't have any that was the right size and strength. It really wasn't helping the trebuchet and I decided to remove it. The launch was much smoother without having a trigger, taking pictures of it loaded was not so easy though.


 * __Conclusion__:**

I reached all of my goals with the trebuchet that I built. I was hoping for a point score of at least 5 which I achieved. I'm not a natural carpenter, but I'm proud that I was able to build something that worked fairly well. There were some portions of the trebuchet that were not built quite as accurately as I would have liked, like the braces and the pivot dowel. The braces are obviously on different angles, neither of them 45°, but they served their purpose well. the pivot was tilted because of my inability to drill a hole in the middle of a piece of wood. This only skewed the direction that my machine shot in, but I would have preferred to build it as accurately as possible. Some of this was caused by the tools that I had access to. Despite any troubles that I had in finishing this project I was quite pleased with my results. I found it very interesting to be able to apply the physics that I have learned rather than only hearing it in a classroom or reading it from a textbook.