Morgan Reynolds on Crash Physics

This is Morgan Reynolds' email from today. It's right on the money.

Lawson vs. Newton:
Newton's 3d law, sometimes called the law of reciprocal actions,
states that all forces occur in pairs and these two forces are equal in
magnitude and opposite in direction. That is, the forces of action and
reaction between bodies in contact have the same magnitude, same line of
action, and opposite sense. Didn't Lawson have a tug of war when he was a
child? If there is a force on the building in a crash, there is an
equal and opposite force on the airplane. Yet the plane does not slow down
or break apart!
If an aluminum plane ran into a Twin Tower, it must crumple, shatter
and could not possibly leave a jetliner-shaped, cartoon-like "silhouette
of passage" because in a collision with a tremendously strong
building, arguably the strongest in the world, an airplane with its far lower
mass, density and strength because it is built to be lightweight, would
be far less able to withstand the equal force exerted on both bodies.
The airlines weigh your luggage and worry about its distribution en
route while building security personnel and custodians do not worry about
the weight building entrants bring in or where they distribute it
because buildings do not have to be lightweight and are built with redundant
strength.

Strength and massiveness matter greatly in which body will fare better
in withstanding the equal force of an impact. Everybody knows this in
shopping for a car: should I buy a heavy SUV for safety or accept the
risk of driving a lightweight econobox or sportscar? If the damage
inflicted on the other body in a collision between a jetliner and a Tower
were likened to a sports contest, it would be something like Tower 100,
Airplane 2. Imagine, for example, that a Tower fell on the airplane
instead of the aluminum airplane hitting the Tower: complete and utter
devastation of the airplane. However, this mismatch is not what the videos
show. Instead, the aluminum plane cuts right through steel and
disappears inside the Tower. This is impossible. Structural steel is far
stronger than aluminum and present in abundant quantities, and would suffer
only light damage compared to complete and utter destruction/rejection
of an aluminum airplane, with most of its debris scattered outside the
building, especially wings, tail section and a majority of the shattered
fuselage. The five floors in each Tower allegedly impacted by planes
weighed more than 100X that of the alleged 140 ton airplanes.