Nat Hager III wrote:
>
> I saw a similar article on a BBC site shortly after the attack, which was
> devoid of ifp but characterized all the various events in terms of Joules.
>
> I explained to my intro physics class as Newton's 2nd law problem. Under
> normal circumstance the 109th floor supplies an upward normal force to the
> 110th floor to counteract the 110th's downward weight mg. But when the
> 110th starts to fall the 109th must supply an ADDITIONAL force ma to
> decelerate the falling 110th floor to rest. This additional force exceeds
> the design requirements of the 109th so it begins to fall, and the problem
> only gets worse as each additional floor adds to the mass and pancakes the
> whole way down.
>
> Of course the physics is the easy part. Trying to explain it to a class
as
> a cool dry physics problem is the hard part.
>
> Nat
Jim Frysinger wrote:
>>>
Yes, indeed. I pointed out to my students, in whatever voice I could
muster, that although it seemed a bit macabre to analyze such an event
there are two benefits that come to mind right away. First, it can help
seismologists quantify the outputs of seismometers, helping to pin down
the relationship between the Richter scale (which we discussed here some
time ago) and energy. Second, and more importantly, it can help
architects design even sturdier buildings, capable of better
withstanding such atrocious acts.
Jim
>>>
>>
I actually felt a responsibility to explain it to the students. Explaining
the dangers of the situation in terms of basic Newtonian mechanics will help
them better protect themselves should they ever (God forbid) be in a similar
situation in the future. I don't think anyone but the civil engineers knew
what was inevitable in those first few minutes.
Nat
