The preceding note that elicited this response was an ill-fated attempt a joke. Apparently everyone thought I was dead serious when I said "30 lbs rapier", and the irony escaped them. My apologies, and in the future I will try not to be sarcastic.

About the Physics of it:
In addition to the points Valguarnera made, the rapier was designed as a thrusting weapon. The primary strength of the weapon was in lunging & stabbing attacks. The rapier was long, and in a process of one-upping, the rapier got longer and longer. It is meant to be a long rigid spike to thrust through your opponent. It's a heavy cumbersome blade.. But by no means is it 30 lbs! =)

I did learn that those light-weight swords that they use on tv are not rapiers, and not even representative of historical swords. They're just flimsy really light junk that "looks" good on tv.

This, from Conquest on the history channel.