After having set up a trebuchet in my back yard, I decided it would be a fun excersise to predict the range of the projectiles launched. Now, I'm not nearly experienced enough at physics to take into account a hinger counterweight or a sling, so I removed those from the machine.Instead I used a fixed counterweight (8 kg of barbell weights attached to a 0.5 kg bolt) on the short arm and a small cup on the long arm, using a golf ball as a projectile. I set up some calculations (essentially setting initial PE equal to the final KE) to determine the velocity and range of the golf ball. The numbers seem to be perfect for the velocity (I used a high-speed camera and a grid to verify this) at 7 m/s, but it is the range that is inaccurate. I'm launching at 45 degrees from a height of 1.3 meters, which, according to http://en.wikipedia.org/wiki/Range_of_a_projectile" [Broken] should give me a range of 6 meters. In practice, I'm getting slightly less than 5. I assume the drag isn't much of an issue, so what would you wager is causing the discrepancy? Thanks!