A 9/11 Truther just told me that the planes slamming into the towers wouldn't have had much effect, because the planes are primarily thin aluminum, just like a beer can. He even helpfully provided weights (fully loaded 747: 395,000, fuel load: 120,000lbs). My response, with names redacted to protect the retarded (my response incidentally also ignores the structural framework of the aircraft):
At approximately 22 miles an hour, the plane would have the same energy as approximately 6.3 pounds of TNT (note that I used the Truther's figures, and subtracted fuel from the equation).
At the estimated 402 miles per hour that the Twin towers were hit at, (an eminently reasonable estimate, because that's the usual fight speed of such an aircraft), it would have about same energy as just over a ton of TNT. Assuming a 45% loss of energy as per the Truther's figures again, we still have approximately 1167.46 pounds of TNT.
If I throw a f*cking beer can at your head at 400 miles an hour, it doesn't matter that it's a f*cking beer can. In fact, it's beer canness makes it worse for your head, because it's going to come apart and dump all of that energy into your witless dome. And even the skull of a 911 truther isn't thick enough to survive that. The same principle applies to the twin towers and the aircraft.
Add fuel to the mix, and the kinetic energy equation gets worse. Then the fuel catches fire and burns at a temperature that robs the steel of it's structural strength.