The Counterweight and Mechanics of a Trebuchet: An
Investigation on a Medieval Machine
Kristin Light and Sara Packard
Table of Contents
Background
A
trebuchet is an instrument devised in the medieval times as a type of weapon
that flings a projectile to destroy a wall or fortress. Although “the first
traction trebuchets were used by Mohists in
Statement of Problem
The purpose of this inquiry is to find the effect
counterweight has on a projectile.
Literature
The information available pertaining to the trebuchet
retain mainly to “The trebuchet uses
gravity and falling weights to launch its projectiles, which are in a swing at
the other end of a weighted lever. Equations necessary for estimating the
ranges are included” (Porter, 1994) Meaning, the specifics on trebuchet power
exertion has no real potential to our study, as factors tend to be invariable.
As well, “specifics” tend to be general, or “this is what may happen.” Other
articles contain mainly information on the history of the device.
Information has lead to the discovery of velocity effect of mass and horizontal
acceleration of the object. As well, distance information will be accounted
for. Projectile motion will be calculated through mass and accelerate movement.
Displacement will be observed by measurements. Energy will also be seen in its
potential and kinetic states using gravity and mass as a basis point. All of
this information has leaded the discovery to be turned about.
Hypothesis
We
believe that if the trebuchet is kept at a constant launching point, meaning
the velocity stressed on the projectile is the same, the heavier massed
counterweight will exert more force, and thus the projectile will go farther
then the lighter counterweight, which will not create as much force.
Set Up
Materials. Ten feet of 1x1 wood. 10 nails. 1 small metal pole. String. Cloth. Wood
glue. Hammer. Stop watch. Pen. Paper. Measuring tape.
Procedures.
1. Create introduction for lab. 2. Create set up for lab. 3. Obtain materials
for trebuchet. 4. Build trebuchet to scale of desired height, in this case
about 2ft. tall. (Instructions to build the trebuchet are included on http://www.ehow.com/PrintArticle.html?id=2031781)
5. Test projectiles, a deck of Bicycle cards, make sure conditions are
premium for flinging projectile. 6. Test away! Make sure to keep record of time
and range, and any unusual observations. DON’T FORGET TO CHANGE
COUNTERWEIGHTS!!! 7. Complete chart. 8. Finish lab.
Formulas
√(range/time)² + ((gravity*time)/2)²=velocity, (√(s/t)²
+ ((g*t)/2)²=v) will be used to determine velocity of the projectiles.
Data Table
Heaviest Weight = 1.5 kg
Middle Weight = 1.0 kg
Lightest Weight = 0.5 kg
|
Weight |
Trial |
Distance (cm) |
Time (s) |
Velocity (m/s) |
|
Heaviest |
1 |
115.57 |
0.57 |
3.45 |
|
Heaviest |
2 |
144.78 |
0.8 |
4.32 |
|
Heaviest |
3 |
20.32 |
3.39 |
16.61111 |
|
Heaviest |
4 |
38.1 |
1.48 |
2.705 |
|
Heaviest |
5 |
91.44 |
1 |
4.98 |
|
Heaviest |
6 |
60.96 |
1.84 |
9.022 |
|
Middle |
7 |
38.1 |
2.42 |
11.859 |
|
Middle |
8 |
22.86 |
1.02 |
2.247 |
|
Middle |
9 |
93.38 |
1.42 |
6.989 |
|
Middle |
10 |
71.12 |
1.03 |
5.09 |
|
Middle |
11 |
27.94 |
2.42 |
11.86 |
|
Middle |
12 |
5.08 |
3.42 |
16.758 |
|
Lightest |
13 |
84.455 |
1.03 |
5.11 |
|
Lightest |
14 |
71.12 |
0.64 |
3.327 |
|
Lightest |
15 |
71.755 |
0.72 |
3.666 |
|
Lightest |
16 |
173.99 |
1.73 |
8.53 |
|
Lightest |
17 |
22.86 |
2.47 |
12.1 |
|
Lightest |
18 |
43.18 |
1.53 |
7.5 |
Raw Data
Graph
Analyzing the Data
Straight
away, the first observations of the data are staggering. There is no real
obvious trend that can be observed from this data. However, the data must be
observed, and some interesting results have been shown. From the graph
collected by the data, the highest point of velocity normally seemed to be the
lowest point displacement. Is it possible that the displacement received more
speed, and thus less time? The data shows that those times were higher with
those unusual points on the graph. Time did not conflict with velocity, though
it is a main principle in its makeup. Meaning, the velocity of the trebuchet’s
mechanics was not manipulated heavily by how far it was displaced.
As
for counterweights, the main discussion of this lab, the trends were confusing.
The heaviest counterweight showed signs of having the fastest velocity and the
longest distances, but that is only averagely accounted. The highest actual
velocity, along with the longest time, was with the middle counterweight. The
longest distance was in the lightest counterweight. What mechanics could this
contraption be developing to demonstrate these points
of data? Regardless of the answer, these observations show that no actual
trends were developed with the use of counterweights.
Errors
The
most important error observed was that there was no normalcy. There seemed to
be no steady line of consistency within the data taken. Each new firing was a
surprise. Because of this, conclusions, tendencies, or trends could not be
properly analyzed. This inconsistency is a possibility of the swinging arm. The
bolts which kept the block of wood on a steady plane were somewhat loose. This
is a possible mechanical error. Other factors, which were tweaked through out
the testing process, proved that the trebuchet was a mix bag of order.
Conclusion
Well,
the conclusion of this investigation is not crystal clear. Though the
development of thought and enhancement of knowledge on the trebuchet, and the
mechanics of working with a trebuchet were highly enforced, the nature of the
lab was to retain results. As for the results, the errors of this lab could not
lead to any results to counterweights effected the sporadic trebuchet. The real
result of this lab is that trebuchets are not meant consistency weapon.
Questions
How
can counterweight be controlled more to create a more constant information
source? How did medieval knights perfect this machinery while in combat? How
does the sling affect the “flight” of the trebuchet? How gravely does the
counterweight matter? Will Kristin ever finish a lab before the day it’s due?
Bibliography
Mozi. Mojing. 4th century B.C.<http://en.wikipedia.org/wiki/Trebuchet.2007>
Porter,
William S., and Robert E. Tremblay.
“A Medieval example of energy conservation.” The
Physics Teacher 32.n8 (Nov 1994): 476(2). Professional
Collection. Gale.
Chevedden; et al. (July 1995). “The Trebuchet”, Scientific
American, 66-71.
Colby Cosh.
The Report. 30.9 (May 2003): p.8 General
Reference Center Gold.
eHow. <http://www.ehow.com/printarticle.html?id=2031781>
2006.
Links
http://en.wikipedia.org/wiki/Trebuchet.2007 A good basic source on trebuchets. A good place to start.
J
http://www.ehow.com/printarticle.html?id=2031781 Would you like to build your own
trebuchet? This site will tell you
how!!!
http://www.trebuchet.com/ If you need this link explained…you need help….
http://www.youtube.com/watch?v=-wVADKznOhY What not to do with a trebuchet…
http://www.tbullock.com/trebuchet.html Yet another website with experiments that you can do with trebuchets.
http://www.belfry.com/fuzzball/trebuchet/ This site has awesome fuzzballs!
Last revised: May 30, 2008