The trebuchet operates by harnessing the potential energy of a suspended weight, and demonstrates many physical pricipals. There are multiple variables in the design which can be adjusted to optimize range and throw-weight. This model has achieved a range of 120 feet with a 7 lb. rock, so far.
"Hurling" has become a gentleman's sport in Texas, where a active hurling society exists. Work is being completed on "Thor", a Trebuchet with a 100' throwing arm using a 55,000 lb weight. The design should allow the hurling of '57 Buicks. In earlier days some Texas trebuchets have thrown 'astro-aguanauts'.
More information is available in the July '95, issue of Scientific American. Also check out the trebuchet used in Northern Exposure.