Proof of Efficacy Doc. The design of our trebuchet is a trebuchet that is not allowed to be over one meter from one point to another on the machine. We used somewhat thick rubber bands and chained two together so that they wouldn’t snap when the arm was pulled all the way down. The base of the trebuchet is 23.5 inches. The two trebuchet arms are 18.8 inches and are 3.75 inches apart from each other. Our axel is 0.25 inches in diameter and is in a hole 13 inches from the base. Near the top I put a stopper so that the trajectory would fire at a certain angle so that it fires as far as possible. Modifications to the Machine 1. The first modification we made was to have 6 rubber bands in three chains of two. We did this because if it was singular rubber bands they would snap because they would be stretched out too far and there would be too much tension. Also, we found if you have more than 6 rubber bands sometimes the clay ball would detach from the string. 2. We next made a 10g projectile for out trebuchet to fire. We tested many different sizes of clay ball and we found the lighter 10g projectile launched further than other sizes. 3. We made our string that the projectile is connected to 8 inches. The longer string didn’t work great on our machine but it worked on other people's. My group had to adjust our string. 4. Then, we made the nail the string is connected to at a 60 degree angle. The 60 degree angle ended up helping to release our trajectory at a better angle. Also, we changed our nail about three quarters of the way though to be a finishing nail. 5. The load to effort ratio was 1:1. This ratio was ideal for launching our projectile as far as we could get it to go. 6. We decided to give the modification of arm stabilizers a try but mid way through our teacher said that if we added them there might be too much friction and it might hinder the performance of the trebuchet. 7. Another modification we made was that the arms of the machine must be stable or else the trebuchet won’t shoot the projectile very far. This happens because the movement of the arms would cushion some of the force. 8. Last but not least, we found that rubber bands worked a lot better than weights when trying to launch our projectile. The elasticity of the rubber bands was way better than a weight which just pushes downward. CLEAR Paragraph Our claim was that the lower the axle is the farther the projectile goes. In our machine I put the stopper at a good place that allows us to change the height of the axle and the angle that the projectile fires at. We tested this by putting the axle in different holes and firing the projectile three times and recording the distance it traveled. But when the axle was really high up the stopper would cause the clay ball to shoot straight up so we had to lower it just enough so it launched at the best possible angle. Although if the axle was too low it would shoot only up to about 3 meters. During our many tests we found that our machine launched the projectile an average of 8.5 meters when the axle was 13 inches above the base. From that height the least distance it traveled was 6 meters where the furthest it traveled from that height was 10.5 meters. We tried our machine at 15-17 inches above the base and once it got that height our furthest launch was 0 meters. That allowed us to come to our conclusion of the lower the axle the further the projectile goes. Technical Specifications Mass of Projectile: The mass of my groups projectile was 10g. For my group this was the optimal size. This is about the same weight as a tech deck. Horizontal Distance: Our trebuchet shot our projectile 20m. This was the distance of our most recent launch. Time in Air: The time the projectile was in the air was for 1.34 seconds. We used a slow motion video to calculate the time the clay ball was in the air. Vertical Distance (d=½ a t^2) where time is falling time: The vertical distance was 2.2m. It was simple because all we had to do was plug in the numbers we already had besides the time where we just had to divide it by two so it was only the time falling. Horizontal Velocity (v=d/t): The horizontal velocity is 14.93m/s. We used our horizontal distance of 20 and divided that by 1.34 and that was the time. We found it shot the projectile at about 33.5 mph. Vertical Velocity (v=at): The vertical velocity is 6.566m/s this is about 15mph. We multiplied acceleration due to gravity and time to get our solution. Total Velocity (a^2 + b^2 = c^2): The total velocity was 16.3 m/s. We calculated this by using the pythagorean theorem. Angle of Release: The angle of release on our trebuchet was 23.7 degrees. We found this by drawing a triangle to scale using our Vvert and Vhoriz then just put a protractor on the drawing. Spring Constant (k=F/d): The spring constant on the trebuchet is 217.78n/m. We did 9.8 divided by 0.045 to get our solution. Spring Potential Energy (PE spring=½ k x^2): The spring potential energy is 11.859J. To find this we multiplied half the spring constant and the springs expansion squared. Kinetic Energy of the Ball (KE=½ m v^2): The kinetic energy of the ball is 1.421J Percent of Energy Converted (KE/PE): The percent of energy converted from potential to kinetic is about 12%. Selling Points Fires consistently Easy to set up Portable Efficient at throwing items that weigh 10g about 20m