Katherine+&+Renata's+Trebuchet

Swiss Cheese- A Trebuchet Project by Katherine & Renata

__**Intro:**__
The origin of the trebuchet dates back to China in 300BC. Back then it was commonly used for warfare, mainly for reducing enemy fortresses and towns to piles of rock. However, nowadays they are often used for recreational activities and competitions such as pumpkin throwing and physics projects. The purpose of this project was to learn the physics of building a trebuchet and applying that knowledge into actually making one. Since our trebuchet is marked not only on the distance the object travels, but also takes into consideration the weight and arm length of the device using the formula Points=Distance/(Mass x Arm Length), making an efficient trebuchet was quite a challenge.

**__Physics Principles:__**

 * Projectiles**- A projectile is an object which only has the force of gravity acting on it. Therefore, once the Christmas ball is launched it becomes a projectile. Since the gravity affects the vertical motion it causes the ball to trace a parabolic curve, which is a common characteristic of a projectile. In order to obtain maximum displacement the object must be released at 45 degrees.


 * Newtons first Law-** Newtons first law states that an object at rest stays at rest and an object in motion stays in motion unless acted on by an outside force. This applies to our trebuchet because when the weight is released it sets the arm in motion. However, the arm then is stopped but because of Newtons Law the object in the sling still wants to stay in motion which causes its release.


 * Centripetal Force-** This is the force that is required in order for an object to travel in a circular path, just like the Christmas ball did. Without this force, the ball would have fallen out of the sling before it was supposed to.

__Building Procedure:__

 * 1) First we cut four pieces for the base. Two pieces that were 35x6 cm and two pieces that were 17.5x6 cm.
 * 2) We then assembled the pieces into a rectangular base with wood glue.
 * 3) We cut two triangular support arms out of plywood that were 34.5 cm tall with a base width of 31 cm. We cut out the center of the triangle to reduce weight leaving a 6.5 cm clearance.
 * 4) The triangular supports were then attached to the rectangular base with wood glue and a few nails.
 * 5) The arm was cut into a 40x4 cm piece of wood.
 * 6) Bristle board was used to guide the sling once released. The bristle board measured 31.5x25.5 cm with rounded corners.
 * 7) A piece of wood 13x4 cm was cut to stop the arm once released that was placed between the support arms. Another piece 14x4 cm was cut to provide a base for the bristle board placed between the long sides of the base.
 * 8) We drilled 3 holes in the arm to see which would provide us with the best results and found the hole 13cm away from the weight gave the best result.
 * 9) On the arm we placed a loop and a hook on the longer portion of the arm for the sling, we attached another loop at the other end so we could attach the weight.
 * 10) A metal threaded rod was cut 16 cm long so that we could attach the arm to the support system with 6 wing nuts.
 * 11) We attached our counterweight that weighed 520g through the loop on the shorter portion of the arm.
 * 12) We placed two loops at the front of the base so that we could stick a nail through them to keep the trebuchet loaded.
 * 13) To further reduce the weight of our trebuchet we cut several holes 1 inch in diameter along the support arms and the base.
 * 14) For the sling, we cut a piece of yellow felt 13.5x9 cm which we then attached to the arm with string. We also cut two slits in the center of the sling and threaded fishing line through in order to load the trebuchet.

__**Materials:**__

 * 7 wing nuts
 * 1 threaded metal rod
 * 21 nails
 * 6 metal loops
 * 1 metal hook
 * felt
 * fishing line
 * 2 pieces of string
 * 1 steel bobbin (counterweight)
 * 2 35x6 cm pieces of wood (base)
 * 2 17.5x6 cm pieces of wood (base)
 * 1 40x4 cm piece of wood (arm)
 * 1 13x4 cm piece of wood (stopper)
 * 1 14x4 cm piece of wood (bristle board base)
 * drill
 * jigsaw
 * table saw
 * hammer
 * pliers
 * measuring tape
 * scissors
 * wood glue

__Photos:__




__Test Procedure & Analysis:__
While testing our trebuchet, we ran into several problems causing us to make slight adjustments between test trials.


 * Sling**- In the making of our trebuchet, we designed a total of four pouches. Initially, we thought a lightweight kite material would work best because it's slippery. In the end, we found the material to be too slippery as the Christmas ball would fall out before its release point. Our last three pouches were all made out of felt; we tested different sizes to see which one would work best. We found that a 13.5x9cm pouch gave us the best results.


 * Pivot Point-** In the arm we drilled three different holes each at different lengths from the counterweight. They were 7.5cm, 10cm and 13cm away from the end of the arm. In the end, we found that the 13cm hole gave us the best results.


 * Arm Stopper-** We adjusted the arm stopper numerous times before finding the sweet spot. We played with various heights, angles and contact points. In the end, we found a spot that stops the arm at the right time, therefore releasing the ball at its optimal release point.

__Test Trial Data:__
P=d/ml P=3.9/(1.4x0.71) P=3.9/0.994 P=3.9
 * =====**Trial**===== || =====**Mass (kg)**===== || =====**Arm Length (m)**===== || =====**Distance (m)**===== || =====**P=d/ml**===== ||
 * 1 || 1.4 || 0.71 || 3.9 || 3.9 ||
 * 2 || 1.4 || 0.71 || 3.1 || 3.2 ||
 * 3 || 1.4 || 0.71 || 3.2 || 3.2 ||
 * 4 || 1.4 || 0.71 || 4.0 || 4.0 ||
 * 5 || 1.4 || 0.71 || 3.9 || 3.9 ||
 * 6 || 1.4 || 0.71 || 4.1 || 4.1 ||
 * 7 || 1.4 || 0.71 || 3.3 || 3.3 ||
 * 8 || 1.4 || 0.71 || 3.3 || 3.3 ||
 * **Average** || 3.6 || 3.6 ||
 * Sample Calculation:**

This project, although frustrating at times, helped us learn about physics in a hands-on experience. It helped us not only with physics principles learned in class but also with the design process and what goes into making a functioning product from start to finish.


 * Edited by both Katherine & Renata*

Source: http://www.medieval-life-and-times.info/medieval-weapons/trebuchet.htm