Hello there
Oh my, we have to get this out of the "tame" arena now, don't we?
Just how 'un-tame' do we want to make it? Are there any buildings in
your school district scheduled for demolition?
To start with, here are a couple of previous answers about science
fair projects. The subject matter of the experiments has no
relationship to yours but you may be able to pick up a few points
regarding presentation, science fair "theatrics" and a few other
ideas. I have no inkling of what grade you are in but there should be
something for most all levels found there. Read 'em.
http://answers.google.com/answers/threadview?id=255153
http://answers.google.com/answers/threadview?id=261037
Now, for your catapults.
You realize that the term "catapult" refers to any machine that hurls
a projectile. That includes items as simple as a toy slingshot or an
ancient style war machine. - - One of ancient uses of the catapult,
which may well find validity in the modern world, was to return
unpopular ambassadors to their cities of origin.
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We can start here: - http://www.catapults.info/ - "All About
Catapults" - Not only will you find somwthing about the history of
the catapult, but you will find information about how to build them.
On the page containing the instructions, at the bottom, you will find
an article about the 'physics' of motion which includes many of the
viarables you are asking about. For example:
v=velocity
g=gravity (between 9.78 and 9.83 m/s2, or 32.2 feet/sec2)
Additional formula:
1 m/s=3.6 Km/hour
1 m/s=3.281 feet/second=2.24 miles/hour
Energy = force * distance = mass * g * height = 0.5 * mass * v * v
Formula quote from website.
Note that the above formula is irrespective of the units you use; put
feet and pounds in and you get feet and pounds out.
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If the catapult you are building is based on the Roman "Onager,"
(which might be the easiest to duplicate) here is the page for you
when it comes to those technical details you asked about. I wish I
could put this simulator interface here as part of the answer, but I'm
afraid you will have to go there. You will find you can calculate
items such as: Angle when cocked, Angle when resting, Torque when
cocked, Torque when resting, Projectile mass, Beam mass, Beam shape
factor, Beam length, Beam length, Sling length, Pouch mass, Sling
ropes mass, Initial sling angle - plus more.
Now, you mentioned PVC pipe and elastic. The materials, whether wood
or plastic, would be included in "beam mass, length, and other
factors. Since PVC would be lighter than wood, your figures should
reflect that. The same with the other materials AND the same if you
decide to build another kind of catapult. Whatever the math
formulations for your particular machine are, mass is reflected by
weight rather than material.
This simulator is "freeware" which you will need to download and
install. It also means that when you complie the figures for your
presentation, you will be able to print them down from your own
computer which is a good indicator that you did the work yourself
rather than having somebody else do it for you. (just a presentation
tip you can use to your own advantage)
Put in the figures you want, take aim, and give me time to get out of
the way before you fire.
http://www.xs4all.nl/~mdgsoft/catapult/sim/index.htm - "The Onager Simulator"
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Here is a small onager built as a project. You will find figures and
construction methods. These machines can be dangerous. Here are a
few words of warning from the builder of this contraption:
"These machines used by the romans to kill people; even small ones
like mine can be dangerous. I have no doubt it will break several
bones of your hand if the arm hits it at full speed.
Be careful: don't stand in front of it, don't put your head above it
and don't stand behind it. Use a safety zone of at least 200 meters in
front and 75 meters behind the machine (depending on its size). Don't
park your car behind it.
And on the brighter side; don't shoot grapes at your bathroom wall;
they make a real mess."
http://www.xs4all.nl/~mdgsoft/catapult/onager2.html - "My Small Onager"
Perhaps if you leash trained it? Oh, never mind.
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Here is a series of plans for building catapults ranging from the
ultra simple for beginners to advanced. I don't know if you need a
reference such as this but I am including it anyway.
http://icatapults.freeservers.com/plans.htm - Catapult Plan Index -
From "Catapults" - - The site also includes quizes, a message board,
modern uses, etc. Overall general information but not much in the way
of technical information.
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Now, since I do not know your grade level, I am including some items
designed for the younger student but there is still material you can
use if you in the upper school years.
Have you ever considered the relationship between fleas and catapults?
I didn't think so. - - - - I didn't either till I read this. In
fact, I seldom think of fleas at all.
http://www.ftexploring.com/lifetech/flsbws1.html#Better%20than%20Muscles
- "Elasticity and energy conversion in fleas, catapults, and bows"
You will find that the methodology of a flea hop is in many ways
similar to that of a catapult and has valid application in explaining
catapult technology. Also, you may note that inclusion of information
of this kind in your science project, which is different but still
applies, is one of those things which will get your judges out of
"automatic drive" when reviewing your presentation. Yours may be the
hundredth project they have looked at that day. You need to get their
attention. - read those first two answers I referenced.
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You have asked about variables such as elevation and elastic size.
However, the only way to understand them is to understand the basics
of how force, power, torque and energy work together to begin with.
Just in case, I am including this:
For example, knowing what an elevation and elastic strength will do is
meaningless without knowing how 'mass' effects the formulation. They
all need to work together. - "Mass is important for calculating how
quickly things accelerate when we apply a force to them. What
determines how fast a car can accelerate? You probably know that your
car accelerates slower if it has five adults in it than if it has just
one." Here you will learn just how to put all these together. What
you learn to do here would make excellent variable charts to include
with your presentation.
http://science.howstuffworks.com/fpte.htm - "How Force, Power, Torque
and Energy Work" - From Howstuffworks
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This is actually a science project that the designer has put online.
It deals with a trebuchet. You will find the full project including
computations, materials, test results and more. If success can lead
to success, this will be a good reference for you.
http://www.geocities.com/SiliconValley/Park/6461/trebuch.html -
"Welcome to the Physics of the Trebuchet" - By Filip Radlinski
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And last, for a good overview of it all, here is:
"War Engines of the Middle Ages" - You will find descriptions of
types, mechanisms, uses, principles of motive force, original drawings
and plans from the Middle Ages, history, reconstructions and a good
biliography.
http://www.middelaldercentret.dk/warengines.htm
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Now, I hope I understood your question right and I also hope we got
this past the concept of "tame." You have a lot of work to do.
Search - Google
Terms - catapults, physics of catapults, ancient war engines, roman
war engines, war engines middle ages, hurling machines
If I may clarify anything, please ask.
Best of luck with your project. You have picked a good subject,one
which can include history, physics and construction sciences.
Cheers
digsalot |
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