IB PHYSICS 2 RESEARCH PROJECT
J.J. Paulson Ryan Link Daniel Espinoza Jaspar Perkins
| Background | Statement of problem | Hypothesis | Results | Conclusion | Bibliography | Related sites | Return To Research |
Go up Background: The Crossbow has been a thing that many people associate with the middle ages. However, the Crossbow is actually much older than that, some archaeologists have found crossbows in 2,500-year-old Chinese graves, and some historians believe that they existed in China as early as 2000 B.C. (Tracy V. Wilson). Basically crossbows have been around for thousands of years and have gone through the ages of many cultures. The most occurring of these cultures using crossbows have been in East Asia and the Mediterranean (Tracy). Crossbows have been modified and upgraded as much as swords have been and equally or even more important, right up until rifles took over the war effort (Emily). In fact crossbows once were banned by the church because of its ability to upset the balance of social classes by allowing a peasant conscript that has very limited training to very quickly kill a fully armoured and very well trained knight of major social standing (Linda). What made these weapons truly so devastating was the fact that they could punch through very thick armour with each shot. This was accomplished by making a bow very thick and sturdy so that the potential energy of the bow was very large (Tracy) The stiffer the bow, the more potential energy it possessed. However, the problem is that the thicker and larger the bow, the harder it was to draw the string back. Many designs have a crank that draws the bow back with a lever or wheel that allows even the weakest of soldiers the ability to draw a heavy crossbow back, hence, allowing any conscripted peasant the ability to kill a heavily armoured knight (Linda) Cross bow modifications have been developed in many ways. The crossbow used by Sun Tzu, the author on The Art of War, used a very light repeating crossbow that had a crank which pulled the draw-string back while dropping the bolt into the firing slot, it then released and immediately reloaded another (Kallie). It was mainly used to kill lighter infantry because ot the lighter draw-back system and poison dipped arrows (Tracy). Furthermore, the crossbow used by Alexander The Great’s armies used a crossbow that was fired from the hip because of the large kick back (Tracy) (For every action there's an opposite and equal reaction). Their reasons for using the heavy crossbow was to fire bolts through Persian shields and through padded cloth underneath. The Siege Crossbow was used by both defenders and attackers because of its massive potential energy. It actually consisted of a VERY stout wooden bow or even a metal one so that it could punch through the armor plating of a knight or the wooden covers of a hiding soldier (Ralph). Unfortunately, generally the heavier a crossbow the longer it took to reload and fire (Tracy). From this point on I shall be discussing how a crossbow functions. Remember that all of this information has been gathered and selected by me through these sites and book. The crossbow is the product of welding a bow onto a stock with a trigger. A bow functions by use of spring action inside the wood itself. With the use of the formula PE=1/2KX*2, we can determine the spring action inside of the bow. The stock and trigger mechanism are to simply hold the string in place, keep the bolt on line, and to allow weaker individuals to use heavier bows. The bow that we use is going to remain constant, therefore the only change allowed is going to be to draw the string back to different distances. This will result in a variance in PE and eventual velocity of the bolt.
Go up Statement of Problem: We are going to see how much the spring potential energy affects the speed of a bolt.
Go up Hypothesis: We believe that the force of the crossbow bolt being the dependent variable and the strength of the crossbow spring as the independent variable will be directly proportional. The Force of the crossbow bolt graph will be exponentially growing and then levelling off because of the limit to which objects can be propelled and the limit to which a spring can take in and release potential energy. We hope to be able to achieve a maximum input of energy to a maximum output of force provided by the bolt.
Go up Results: The data supports our hypothesis that the more force put into the bow, the more force transmitted to the bolt. Draw lengths 1-5 are fairly linear in that the distance moved each set of trials increases when a longer draw length is used. Calculations: K=.614 ((5.12=.5K7.75*2)+(2.987=.5K4*2)+(7.35=.5K9.375*2))/3=Average K
Go up Conclusion: The data provided by our study proves our hypothesis was correct. Our hypothesis was proven because the farther back the string of the crossbow was pulled, the farther the target was pushed back by the crossbow bolt. Our main sources of error were human error and wind error. If we were able to have a less wind and a more stable platform to fire off of, then our data would be more accurate than the results we got. Upon filming the trials, the wind was slightly gusty, causing our data to vary slightly. Human error is always a factor, and it was present. The bow used was a compound bow which caused our data to plateau. If we were to further our research we could use different kinds of bow, such as a composite bow or a longbow, and bolts of different sizes and weights. The target we shot at could have also been made of a different type of material, like cardboard. In conclusion, this experiment proves that the force of the crossbow bolts is directly proportional to the crossbow spring.
Go up Bibliography: Wilson, Tracy V. "How Crossbows Work." HowStuffWorks. How Stuff Works, n.d. Web. 05 Nov. 2013. Alchin, Linda K. "Crossbow." Crossbow. Lords and Ladies, 16 July 2012. Web. 05 Nov. 2013. Szczepanski, Kallie. "The Invention of the Crossbow." About.com Asian History. N.p., n.d. Web. 05 Nov. 2013. Nickols, Emily. "Smith College Museum of Ancient Inventions: The Crossbow." Smith College Museum of Ancient Inventions: The Crossbow. N.p., 1 Jan. 20000. Web. 05 Nov. 2013. Payne-Gallwey, Ralph. The Crossbow: Its Military and Sporting History, Construction and Use. New York: Skyhorse Pub., 2007. Print.
Go up Related sites: How stuff works: Figured out the basic construction and functions of a crossbow. Also discovered the crank system for stronger force crossbows. Lord and Ladies Discovered it takes years to learn the bow which was a superior weapon and that the crossbow was easier to train young recruits. The Crossbow was also banned by the pope. Invention of the crossbow: Europe designed a heavier crossbow to punch through knights armour. China developed light crossbows that were very quick firing, while the European required a crank which took large amounts of time to cock and fire. Smithsonian: Discovered how old the crossbow was and found out for first time it was present and developed separately in both Europe and China. The Crossbow: Its Military and Sporting History, Construction and Use Discovered different bolts of varying weights and lengths were required for different strength crossbows.