Catapult Construction

[Ultramadscienti]

My class is making catapults to demonstrate physics and whatnot. We only have to be able to toss a tennis ball 8 feet, I can do that; however I want to be able to launch a bowling ball 20 feet (to impress my favorite teacher). I would like to know what you would suggest as the component that would provide the force.

[DonRotolo]

Catapults are powered by springs or the like, as compared to a trebuchet which uses a weight and gravity.

Some ancient catapults used several strands of heavy rope, attached to the frame and the arm, which were tensioned by turning a ratcheting mechanism on the frame. You can see the twisted rope surrounding the axle in this image.

Other catapults used the energy stored in the bending of the arm. See how this wooden arm is bent after being pulled down by the rope?

In ANY CASE, be sure to consider what will happen when the arm breaks. Release mechanisms must be operable from a distance, and much stronger than you think. Make sure you stay safe please.

[Ultramadscienti]

Would rope or surgical tubing make a better mechanism for making the arm swing?

[DonRotolo]

That's for me to know and you to (experiment and) find out.

[Ultramadscienti]

Curse thinking for myself, curse it to... actually I should run a script to see how would be the most efficient way to curse it.

[davidthefat]

Apparently there are many many different ways you can make a catapult: http://science.discovery.com/tv/punkin-chunkin/

[PAR_WIG1350]

Trebuchets ARE catapults. The difference is trebuchets are gravity powered catapults rather than torsion catapults. Also, despite the bend in the arm, the second picture appears to be a trebuchet, or a hybrid catapult.
You will probably get more out of surgical tubing then rope. Using both might be even better. also, not to discourage you, but bowling balls can break if dropped/bounced. It happened once on Mythbusters.

[DonRotolo]

Originally Posted by Ultramadscienti

actually I should run a script to see how would be the most efficient way to curse it.

That would be cool. Post the results here.

Originally Posted by PAR_WIG1350

despite the bend in the arm, the second picture appears to be a trebuchet

Yeah, maybe, but I picked that image because of the bend in the arm, nothing more.

Catapults are a class of things to fling things. Trebuchets are in the Catapult class. Do not fling cats, please (even though they make a wicked cool "pult" sound when they hit)

No animals were harmed in the making of this post.