From: sichase@csa3.lbl.gov (SCOTT I CHASE)
Newsgroups: sci.physics
Subject: Re: Question about falling elevator...
Date: 11 Sep 92 18:23:57 GMT
Organization: Lawrence Berkeley Laboratory - Berkeley, CA, USA
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In article <88580@netnews.upenn.edu>, owens@hilbert.wharton.upenn.edu (Susan Owens) writes...
>Hi,
> 
>  I have a question that I thought maybe someone here could answer.  It
>concerns a falling elevator.  If I was in an elevator that was falling
>say 20 stories what would happen if I jumped right before I hit the
>ground.  I say that I wouldn't be able to jump because of the force
>being exerted against me, some collegues here say that I  would be able
>to jump but that I would not affect the force with which I hit the ground with
>to any degree to be worth mentioning.  I agree with that but I still say
>that I would not be able to jump. 

The answer depends on how realistic you want to get.  Consider the following
versions of the problem:

(I) Ideal elevator, i.e, no resistance to the walls of the shaft.

In this case, you cannot jump, because you are in free-fall with the 
elevator and cannot crouch down for the jump.  

(II) Ideal elevator with a handrail.

If you are clever, you could press up on the handrail in order to crouch
down for the jump.  In this case (probably not considered in your argument)
you could jump even in an ideal elevator.

(II) Real elevator, i.e., some resistance to the walls of the shaft.

In this "real-world" case, you *can* jump, because the elevator is not
in free-fall, and you will still feel some net gravitational force 
which drives your feet into the elevator floor.

> And if I am right I am sure that there is a less distance that I  
>could fall that I would be able to jump right before I hit the ground
>(I would say roughly around 4 stories).  Does anyone know the aprox.
>height at which an avarage person would be able to jump before hitting
>the ground. Or maybe I am totally wrong (wouldn't be the first time) 

Jumping won't really help you because you are not strong enough to
deccelerate nearly enough to prevent your death.  But the minimum
fall height which would give you enough reaction time to do so would
depend on how much friction the elevator feels as it falls.

Much confusion has been caused about this question by the cartoon people,
who like to have Bugs Bunny step off the falling rock just in time to 
aviod being dashed to pieces along with Elmer Fudd.  

BTW, Mr. Otis made his fame not for inventing the elevator, but for
designing the automatic braking mechanism that passively prevents elevator
free-fall in most circumstances.  This significantly increased public 
confidence in the contraptions and decreased accidental deaths.  I would
think that many more people die due to faulty door mechanisms (like what
happened to Rosalyn on L.A. Law last year) than they do from elevator crashes.

-Scott  

--------------------
Scott I. Chase			"The question seems to be of such a character
SICHASE@CSA2.LBL.GOV		that if I should come to life after my death
				and some mathematician were to tell me that it
				had been definitely settled, I think I would
				immediately drop dead again."      - Vandiver
Newsgroups: sci.physics