I'd keep the info on building very brief and just try to give an overview of the wide variety of different bows from different cultures and what a bow can do.
Emphasise the simplicity of the device yet it's world changing impact... imagine being the first man to harness stick and string.
Whatever you do, put it in terms that people can relate to.
Like quoting speed in mph not fps.
I find that people can appreciate the power when I say even my small flat bow could shoot an arrow through a car door. Cover the broad spectrum from a native American driving an arrow through a Bison from the back of a horse to an English bowman drawing about 170# and shooting through French armour.
Ask 'em how far they think a Turkish flighbow from the 17th century could shoot (about half a mile!).
Some of the stories recounted in a previous thread about a hand gun shot at a bucket of sand which stops the bullet vs an arrow which penetrates are good too.
I like to point out that although it's a very simple device the maths and physics of it is rather complex. Tell 'em there is one more device which is also lethal, but even simpler, and has only one single part yet is extremely difficult to analyse but is made by so called primitive man.... see if they can guess what it is.
Del
(Oh yeah, at the end you let 'em off the hook and tell 'em it's a boomerang!)