The Physics of the World Trade Center tragedy

The Physics of the World Trade Center tragedy

Did the terrorists know this would happen. No. This was a new mode for the collapse of a tall building that was completely unanticipated. I can't rule out that some engineer, sometime, didn't write a memo pointing out this failure mode, but it was not well known. If it were, the building would not have had 300 firemen in the building at the time of collapse.

It is the fire that eventually caused the buildings to collapse. It was not the impact of the plane; it was not the explosion.

Will this happen again?

No. A commercial airplane will probably not be used as a weapon in the United States in the foreseeable future. The reason is simple: without the cooperation of the pilot, the attack is very difficult to accomplish. If the pilot keeps the cockpit door locked, the hijacking suddenly becomes much more difficult. Remember, the only weapon the hijacker had was a knife. In the past, this was sufficient: threaten a passenger, and the pilot will do whatever you ask. In the future, no airline pilot will let a hijacker take control of the plane.

-----------------top----------

Terrorism of September 11, 2002

(combined with previous chapter: dropping food without parachuttes, on 3-17-02)
© 2001, 2002, Richard A. Muller

Last Tuesday, terrorists attacked the World Trade Center in New York, and the Pentagon in Washington D.C. In the spirit of this course, I'm going to describe what happened with emphasis on understanding the relevant physics. This should give you a somewhat deeper appreciation of the problems involved in countering terrorism, and in finding the solutions.

Choice of flight

The terrorists chose to use the fuel of the airplane as their weapon. They chose transcontinental flights since these flights would have full fuel tanks. The airplanes probably contained 60 tons of fuel each, maybe more. Airplane fuel contains 10x the energy, gram per gram, as TNT. Thus the energy was equivalent to about 600 tons of TNT, more than half a kiloton. However, fuel doesn't explode unless it is well mixed with air. We'll describe what happened in the impact in a later paragraph.

The terrorists chose early-morning flights. This was possibly because, in the U.S., such flights have the best on-time records. The terrorists wanted to have several attacks take place almost simultaneously. Their scheme would work only if the flights left on time.

Terrorists board the airplanes

The planned attack took advantage of basic knowledge of airport security. But this was not a deep knowledge; it was known to almost any technically-competent person.

When you board an airplane, your carry-on luggage is passed through an x-ray machine. It can spot many objects from their shapes, although they don't have good enough resolution to see an object which is camouflaged. I suspect no camouflage was used, because if caught, that would suggest that a terrorist attack was underway, and might alert the security people.
----------------
.../...

Impact

As the airplane entered the World Trade Center building, it was torn apart, and the 60 tons of fuel, stored mostly in the wings, was released. Such fuel is highly explosive when mixed with air, but the mixing is not easy to accomplish. Only part of the fuel exploded. (Technically, it was not an explosion, but a conflagration. That's why the sound was muffled.) Most of the force of the explosion blew out several floors of the World Trade Center. The explosion passed around most of the columns, leaving them in place. (The only columns taken out immediately were probably those hit by the plane directly.) Much of the airplane passed through the building and emerged on the other side. This may be why debris from the airplane (including the passport of one terrorist) was found; it was not trapped in the building itself.

The buildings survived the impact. As you look at the films, note how little the upper parts of the buildings move. The antenna on the North Tower hardly shook. The upper part of the building remained vertical. Even the windows didn't break. Neither the impact, nor the subsequent explosion, destroyed the building.

The Fire and the collapse

The steel columns were covered with insulation, and were designed to maintain their strength for 2 to 3 hours of burning. However, the material that burned was not office furnature and paper documents. The wings, with their fuel load, probably remained in the building, where they provided fuel for the subsequent burning. The fierce burning that took place over the next hour was slowly fed by the fuel leaking out of the remains of the tanks.

At high temperatures, steel will melt. At much lower temperatures, it weakens. The jet fuel created a holocaust far hotter than planned for in the building. When the columns weakened, they became vulnerable to buckling. When buckling takes place, it takes place quickly. When one column buckles, it puts more weight on the others, and they buckle too. The columns for an entire floor (maybe for several floors) buckled at one time. The upper floors then slammed into the lower floors. The impact multiplied the force on these lower floors, and they buckled. The process continued as each lower floor continued to buckle in turn. In a few seconds, the entire building had collapsed.

Did the terrorists know this would happen. No. This was a new mode for the collapse of a tall building that was completely unanticipated. I can't rule out that some engineer, sometime, didn't write a memo pointing out this failure mode, but it was not well known. If it were, the building would not have had 300 firemen in the building at the time of collapse.

It is the fire that eventually caused the buildings to collapse. It was not the impact of the plane; it was not the explosion.
=============
this is such a farily tale, obfuscating the huge cracks in the 'story' ....
and these "students" are in high school? NO DOUBT there are kids ALL across the USA that learn more Physics than this, WITHOUT getting near an AP class./js
==============
For physics majors only: In the MKS system, a kilogram is a unit of mass. However, in common usage, we say the "weight" of a kilogram of mass is also a kilogram. Even physics professors do this. In Europe, if you buy a kilogram of potatoes, you get potatoes that have a mass of a kilogram, which weighs 2.2 lb. The force that this kilogram exerts on the table that is holding it is, technically speaking, 9.8 "Newtons".
Where are the student so totally stupid that only a "Physics Major" is expected to carry-through an EIGTH-GRADE ALGEBRA equation. Hello? Are all these folks droupouts? or worse? UC BERKLEY? and they have zero security on the web files? Look, here is the final exam, etc: http://muller.lbl.gov/teaching/Physics10/

http://muller.lbl.gov/teaching/x7cfolder/7cfinal1997.GIF
==================

WHAT A MORON

http://muller.lbl.gov/teaching/Physics10/old%20physics%2010/pages01/TerrorismOver.html

So here is my scenario. Shortly after the airplane attacks, the terrorists saw that the international police cooperation was occurring much faster than they had expected. Many of their people were being arrested. They decided to launch their second wave immediately. It was designed to be so widespread and devastating that it would completely intimidate the world, and result in great pressure being brought on the US not to attack Afghanistan. Letters to Tom Brokaw and the New York Post were postmarked September 18. On September 21, a petrochemical plant in Toulouse France suffered an explosion that killed 29 people, injured several thousand, and destroyed numerous buildings. A warehouse that contained 300 tons of ammonium nitrate fertilizer is now a 150-foot-wide crater, surrounded by debris. A tie to the U.S. attacks is suspected, but the evidence is all circumstantial. See the New York Times account. Other attacks were planned (e.g. an attack on the US embassy in Paris) but failed because of rapid police action.

But the main assault was going to be anthrax. The lethal dose of anthrax is about one billionth of a gram! One gram could kill a billion people. How devastating would be a single gram placed in an envelope? Everyone in the building would die -- or at least that is what they probably expected. Maybe even the entire area would be contaminated. The first mailings appear to have been directed at newspapers and TV news personalities.
==================
http://muller.lbl.gov/teaching/Physics10/old%20physics%2010/pages01/NatureofWar.html

The US military does not believe that Afghanistan will be a quagmire. They have studied the Russian experience, and will do things differently. They will take out all advanced weapons quickly. Remember, when the Russians were there, they had to face an enemy that was being resupplied by us. Nobody is going to be resupplying the Taliban. The US will have AWACS and other radar, U-2s, and drones constantly surveying the countryside. There are no jungles in Afghanistan.Troops can hide in caves, but they will be seen when they move to a new cave. Small arms will survive, and snipers will be a constant problem. In the past, a few deaths from snipers would have brought the US troops to a standstill. Things are different now. We will take the casualties, and take out the snipers.
============
http://muller.lbl.gov/TRessays/03_Al_Qaeda_Anthrax.htm 4/16/2002

Although the evidence remains circumstantial, most experts continue to believe that the anthrax terrorist was a disgruntled U.S. citizen, working alone, trying to frighten and kill, or perhaps to probe our biological warfare defenses. Much of this theory is based on handwriting analysis of the anthrax letters, along with reports that the anthrax was the American Ames strain, apparently refined for military use. Barbara Rosenberg of the Federation of American Scientists gives an extensive review of the data (see her Analysis of the Anthrax Attacks at the FAS website), and argues that the FBI knows the identity of the perpetrator but is keeping it secret, perhaps to protect classified programs.

.../
f mass anthrax deaths were part of the perpetrators' plan, how did it go so wrong? I suspect that the terrorists were influenced by the misleading technical concept of "lethal dose." Consider the following paradox: Senator Patrick Leahy, after a briefing on the possible contents of the letter sent to him, announced on Meet the Press that it might contain "100,000 lethal doses." Yet only five people died from all the letters. Was Leahy exaggerating? No. He was being conservative. How can we reconcile five with 100,000? Based on primate experiments, the Defense Intelligence Agency estimates that 2,500 to 55,000 spores are enough to trigger fatal pulmonary anthrax infections in half of those exposed (the dose epidemiologists call "LD50"). It is possible that any one spore can trigger the disease, but the probability is low, so many are required, on average. Ninety-four-year-old Ottilie Lundgren, the fifth and last victim, may have been killed by just a few spores. That would explain the absence of detectable anthrax in her home and belongings.

My opinion is in the minority—in fact, the tiny minority. According to the October 27 Washington Post, a senior official said "nobody" believes the anthrax attack was the second wave. "There is no intelligence on it and it does not fit any [al Qaeda] pattern." But whether it fits the al Qaeda pattern depends, in part, on the intended scale of the carnage. It may be a mistake to assume the attack worked out as planned.
=====================

==== ===
flapping lips continues:

http://muller.lbl.gov/TRessays/06_Afraid_of_1984.htm

Orwell's error was remarkably simple: he assumed that only the state would be able to afford high-tech -- an assumption shared by virtually every prophet, science-fiction writer, and futurist. But it has proven to be wrong. As late as the 1970s, the driving force for electronic technology in the U.S. was the military; now the Department of Defense has difficulty getting industry to respond to its needs, since they are dwarfed by the consumer market. The military, whenever possible, now orders commercial off-the-shelf technology rather than “mil spec.” Many of the GPS receivers used in Desert Storm were bought at Radio Shack. Radios have become so inexpensive that Intel is now planning to engrave a miniature one on the corner of every silicon microchip, at no extra cost (see "Radio Ready Chips," TR July/August 2002). Most of us cannot even count the number of computers we own, because we don't know how many are hidden in our microwave ovens and automobiles.

To be sure, technology has introduced problems. Like anything out of control, it does not always lead us where we want to go. It is particularly difficult to predict its long-term effect on the environment. But in a time when technology is frequently under attack, it is worthwhile to notice its role in spreading truth. It was not Stalinism, but the flow of information that proved to be unstoppable.
==========
http://muller.lbl.gov/TRessays/12_Inspections_as_Expected.htm

terd brain spews:

The United Nations inspectors will not find illegal weapons in Iraq -- at least, not until after the war.

by Richard A. Muller

Technology for Presidents

from Technology Review Online

January 10, 2003
.../...

The U.S. has other information that it has not yet revealed, either to the United Nations or to the public, presumably including the location of suspected clandestine sites. This is what likely gives President Bush his confidence. Despite demands from pundits, he is wise to hold such information close, while the U.N. gathers additional information. When he finally releases U.S. intelligence, the inspectors will go to the suspect sites, and war will likely follow quickly.

A new and important stage in the confrontation began this week, when the U.N. started using six helicopters, three American and three Russian. These allow swift inspections of remote sites, and they will probably be used in the last pre-war inspection. That may not take place until the U.S. is war-ready. This inspection will be directed at a secret site, perhaps an underground facility, perhaps a remote palace, a location that the inspectors previously ignored. We can anticipate that Saddam will not let them in. His rhetoric will be intense. He will claim that the inspectors were trying to humiliate him, and that he had a sovereign right to keep them out. But shortly afterwards the war will begin, very likely with Security Council approval. War can still be averted. The most likely way, one that is being encouraged by the United States, is for Saddam to be overthrown by his own people. The Iraqi military knows it cannot win, and does not want to experience the devastation of another U.S.-led attack. Ironically, Saddam may be inadvertently encouraging a coup through his repeated claims that war with the U.S. is inevitable.

There are other scenarios that avert war. If the inspectors are given complete access to every site they suspect, then there will not be war. (Some pundits think President Bush will attack anyway, but I do not.) Or, perhaps Saddam will relent and admit to having weapons of mass destruction -- and then disarm. But this doesn't fit with what I and many others have perceived in Saddam's character.

I think Saddam has weapons of mass destruction, and that he will not allow the U.N. inspectors to find them. The goal of the inspectors is not to find these weapons, but to be denied access. When that happens, they will have succeeded in their mission. War is next. Vindication will come only afterwards, when the illegal weapons sites are found and destroyed. At least, that is what I hope. I fear that the first compelling proof of Saddam's weapons of mass destruction may come, not after the war but during it -- when Saddam demonstrates their existence by using them.

Richard A. Muller, a 1982 MacArthur Fellow, is a professor in the Physics Department at UC-Berkeley where he teaches a course entitled, "Physics for future Presidents." He is also a faculty senior scientist at Lawrence Berkeley Laboratory.