Background Information:

The Affects of
Different Lengths of
String on Guillaume

Elli Ramirez

Kenneth Jaimes

And Zachary Munger

Physics II 3A

Table of Contents:

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Background Information:

Trebuchets were the most dominant siege weapon before the emergence of dominant gunpowder. They are most commonly associated with the medieval time period and their most common use was to breech the fortified walls of a castle from a relatively long (and safe) distance away. Trebuchets are also known to have been used in the earliest forms of germ warfare – an attacker would send some diseased body over the fortifications of a castle and the city would then be infected³. The Chinese are credited for the creation of the first trebuchets between the fifth and third centuries BC. Trebuchets were the successors to catapults and they were fundamental in the conquests of the Mongol and Islamic expansions¹. These ancient war machines proved their worth by being dominant in warfare for about a thousand years².

A trebuchet is set up like a balance and functions through a similar set of physics. One end of the trebuchet is a long, lightweight, and strong arm with a sling attached at the end. On the other short at reinforced end, a swinging counterweight is attached and weight can be added into the bucket-like counterweight. The common ration of distance between the long and short arms is usually between a 3:1 or 5:1 ratio. The short counterweight side is suspended up into the air (giving it a lot of potential energy) while the long end is fastened to the base of the trebuchet with a latch. When the latch is released, the potential energy turns into kinetic energy as the counterweight drops and the long arm is swung up. In this motion, the sling releases its projectile forward. There are a ton of different variables in the physics of the trebuchet including, but not limited to, the mass of the counterweight, the ratio of the arm lengths, the length of the sling, and the mass of the projectile. For the purpose of this experiment, we’ll be focusing on how the length of the sling will affect the range of the projectile. The length of the sling affects the range of the projectile because it affects the release point of the projectile.

Brainstorming how our trebuchet would function originated from Ben Hewitt’s “Cheap trills⁴.” The construction of our trebuchet will be based on the models and plans of Kevin A. Geiselman⁵.

Statement of the Problem:

The purpose of this investigation is to determine the effect that the length of the sling has on the trebuchet’s horizontal range. The length of the sling alters the release point of the projectile, which in turn, affects how far the projectile is launched horizontally.

Hypothesis:

Our results will resemble the shape of parabola graphically, with the shortest and longest lengths having the least range. We will try and find the length of sling that provides the greatest range for the projectile. When graphed, the independent variable will be the length of the string, while the horizontal range of the projectile will be the dependent variable.

Materials:

Procedure:

1. Research plans to build a trebuchet. There are lots of plans online, and our group chose the plans we did because it allowed us to test the variable we wanted to alter and it was pretty open ended which provide us with the opportunity to think more creatively.

2. Construct Guillaume. Or whatever you choose to name your trebuchet. Construction can take a long time, so plan ahead.

3. Cut out holes in the leather sling so that you can slip the string through easily.

4. We made strings of 25, 35, 45, 55, and 65 inches in length in two sets. About three inches of each string will can be slipped into the sling or taped to the trebuchet arm. If you subtract three from the string length and divide that number in half, you’ll end up with the length that runs from the trebuchet arm to the sling.

5. Tape the string of 11 inches to the trebuchet’s arm.

6. Tape the string firmly to the trebuchet.

7. Cock and launch the trebuchet.

8. Measure how long the golf ball was launched.

9. Repeat the Steps 7 and 8 until you have eight data points.

10. Repeat Steps 5 through 9 with each of the other strings.

The Data:

Data Files: Text | Excel

Conclusion:

The data supported our hypothesis. When graphed, the data resembles a bell curve and it’s clear that the string length affects the launched horizontal distance. The ideal string length for Guillaume is between twenty-six and thirty-one inches. Further testing of the string lengths between twenty-six and thirty-one inches would be required to precisely say what the most ideal string length is for Guillaume. Based on the data we collected, we could conclude that the ideal string length is closer to twenty-six inches rather than thirty-one inches. The length of the string length is significant because it alters the release point of the trebuchet.

Because there is no “standard” trebuchet, we can’t say that the ideal string length we found works best for all trebuchets. However, for further research, we could see if we found the ideal ratio of sling length and arm length, or sling length to height of the trebuchet. Such research would require many more trebuchets of varying sizes.

There are numerous things factors that created experimental error for us. The biggest, in our opinion, was the surface that we tested on. When we initially tested our trebuchet, we were launching on the turf field. But when we actually tested our data, the turf field was being occupied and we had to test on a very rugged and uneven field. We were forced to test on this field because it had 5-yard markings. The infinite potholes and divots in this field often added weird spin to the golf ball or stopped it’s momentum completely, whereas when we launched from the turf field, the ball launched about twenty yards further. If the field consistently affected the ball, then this wouldn’t have been an issue. But the affects on the golf balls were unpredictable and we would for sure test on the turf field next time.

Mechanically, our trebuchet functioned quite consistently and the change in release point did change as we predicted. However, our measuring techniques were flawed. The turf field at the high school has markings at every yard, which would have helped made our recordings more accurate. But the old field we had to use only had markings every five yards.

We also had a very small counterweight basket. When we built it we just followed the instructions given. But we not know that a larger basket would have allowed us to add more weight to the counterweight. Out counterweight was often overflowing with weights, and sometimes these weights would drop out of the basket when the trebuchet was launched. We assumed that this would have altered our data only if the weight dropped out of the basket before the projectile was launched

Again going back to the field – it had rained the day before we gathered our data and the field was still wet and even muddy in some parts. When the ball would bounce on a slick part, it wouldn’t slow down as much as it would if had ran into a ditch. Weather wouldn’t have been an issue had we tested on the turf field because, again, the evenness of the [communist] turf field would have created an equal experience for every golf ball launched.

-Viola!

Bibliography:

Chevedden, Paul E., Les Eigenbrod, Vernard Foley, and Werner Soedel. "The trebuchet." Scientific American 273.n1 (July 1995): 66(6). General Reference Center Gold. Gale. Tualatin High School. 29 Oct. 2008

Johnson, Howard. "Big hurl." EDN 50.15 (July 21, 2005): 30(1). General Reference Center Gold. Gale. Tualatin High School. 29 Oct. 2008
<http://find.galegroup.com/ips/start.do?prodId=IPS>.

Kibble, Bob. "Physics under siege: a trebuchet exploits the principle of the lever to hurl missiles. By considering the conservation of energy, we can predict the launch speed of a missile. Analysis of the resulting projectile motion enables its range to be found." Physics Review 14.4 (April 2005): 26(4). General Reference Center Gold. Gale. Tualatin High School. 29 Oct. 2008
<http://find.galegroup.com/ips/start.do?prodId=IPS>.

Hewitt, Ben. "Cheap trills." Popular Mechanics 183.10 (Oct 2006): 72(4). General Reference Center Gold. Gale. Tualatin High School. 29 Oct. 2008
<http://find.galegroup.com/ips/start.do?prodId=IPS>.

Geiselman, Kevin A. "Medium Trebuchet." Ingenium Ingenious Machines (Aug 2006. 29 Oct. 2008
< http://www.tasigh.org/ingenium/medium.html >

Links:

Building Instructions - Provided guidelines on how to build a trebuchet

The Trebuchet - History of trebuchet

Cheap Trills - Other inspiration for a trebuchet