Physics Project

[Saturn]

For my physics class we are to start a group and build a catapult. By October somethingish (I can't find the sheet) we must have one that can launch a 10 lb pumpkin at least 40 yards. A friend and I are designing it while the others do the other recording and grunt work. We decided on making a trebuchet. We have a disagreement, however. He wants to build a simple fixed-counterweight style one and I want to build a hinged or pivoting counterweight to maximize downward force and I want to put wheels on it to maximize distance. He wants to beat a certain team, but I want to win the whole distance thing. I want to go full size with a counterweight of 1330 lbs. Anyone know how to figure the max distance and know some designs I can find on the web? I'm really pysched and want to go all out while my group just wants to half ass it and get it done. Beyond a certain distance we get extra credit so if I can get 400 yards I wouldn't even have to work the rest of the term. Dressing up in custom also gets us more extra credit. Give me adive please! This is so cool. I hope to go over the whole football field and across the road into the neigboring cornfield and show up the whole physics class and break the school record. I know I can. I hate groups and I wish I could do this myself...

[GeneralChaos]

Its fun to mess around with, but 1330 seems a bit much. You still gotta lug that crap around. What I'd do if I were you is build a scale model and throw a tennis ball or something with like 10 lbs, then estimate the weight for the final version.

Anyway, I'll bookmark this and post more details, but if I remember correctly:

a b
_______
/\

From a television show on pumpkin chucking, I seem to recall they suggest a ratio of b:a should be between 1:4 through 1:7. This means, every 1 lb on B translates to 4 lbs on A. I know nothing about ballistics, but I'd imagine if you work out the amounts of force you could find something to give you an idea of how far it'll go. Anyway I'll hunt for stuff to post tomorrow.

[ajm317]

Well, clicking through the links on Wikipedia I came across this:

http://www.algobeautytreb.com/trebmath35.pdf

This goes through the mechanics of a trebuchet pretty in depth. It starts out simple enough, but then it goes to a Lagrangian formalism, and finally tosses in constraints on top of that. I don't know what level of physics you're taking, but I'm guessing you haven't seen that stuff.

Anyway, if you can't follow the differential equations and whatnot there's an interesting table on page 20. What it basically states is that with a CW of 100 lbs, a projectile of 1 lb, a short arm of 1 foot, a long arm of 4 feet a hinged cw of 1 foot and a sling of 3.25 feet and a beam that weighs 5 pounds you can get a range of about 230 feet.

Also interesting is the conclusion on page 40, which basically tells you what you need to do to build a good trebuchet.

[chriscase]

One thing to keep in mind about projects is that many times the most ambitious plans for a project do not get realized because the project does not get finished. Better to design a minimal device and then add features as time allows.

Also, since this is a physics project, I'd think you would do better to at least try to work out the physics (at the level you are currently studying) yourself. I'd guess that will be some basic levers and F=ma.

[Captain Kirk]

One thing to keep in mind about projects is that many times the most ambitious plans for a project do not get realized because the project does not get finished. Better to design a minimal device and then add features as time allows.

He speaks the truth. The only rule in my colleges Engineering societies contest is 'no engineering'. Of course this is an overstatement, trebuchets can go wrong so easily. Viking catapults are pretty good though, im told