From: chrism@cirrus.com (Chris Metcalfe)
Subject: Helmets and Stones
Organization: Cirrus Logic Inc.
Date: Fri, 24 Jul 1992 18:22:45 GMT

As a rock-climber I know that a rock of 1-3 pounds falling 25-meters is lethal.
Rock-climbers generally wear helmets to protect against stones accidentally dislodged
by the lead climber.  The professor who introduced me to climbing had this advice
however:  if a stone is dislodged (the lead climber yells "rock!" if he notices
it) you should cover your head with your forearms (even if wearing a helmet).  Your
arms will definately be broken, but they may absorb enough of the energy that your
head might survive.

Getting off of a technical route with broken arms is what climbers call an "epic."

-- Chris Metcalfe

In article <1992Jul24.020248.23277@wpi.WPI.EDU> nyh@emilio.WPI.EDU (Nevo Y Hed) writes:
>In article <1992Jul23.215254.16589@colorado.edu> 
>perlman@qso.Colorado.EDU (Eric S. Perlman) writes:
>[...]
>>The rocks I remember from the video looked to be 2-5 inches in diameter.
>>That still means a rock weighing 1-3 pounds (you're talking about
>>something the size of a baseball or softball but several times as
>>dense).  These thrown as hard as possible over a wall, and having a
>>20-30m drop down to the plaza in front of the wailing wall.  Considering
>>that fastballs which hit on the head can cause rather severe injuries,
>>and that these rocks are both heavier and have 20-30 meters of height,
>>that's a significant danger.  Not as significant as a bullet, but pretty
>>significant nevertheless.
>
>OK ... Lets make it more official - I have dran here [with my
>emacs-art talent] a description of the travel of a stone.  I am sure
>that there are many people here that are more experts then myself in
>physics.  I didn't trust myself with alculating V3y.  If noone will
>dare at this chalange I will lookup my physics book and try not to
>fu**up or ask my dad.  We also need astimates for V1x & V1y - I am
>taking Eric's etsimate for H - if you know a better number - go ahead.
>After we get a final number for |V3| we can then ask any ol' MD what
>it actually means if it hits someone in the head.
>
>
>
>
>	
>                        __--------__
>                      _-            -_
>  V1y                ~ 	              ~
>       	            '	               `       ---> V2x  |
>  ^       _        /                    \                |
>  |   V1  /|      /                      \     \         V V2y
>  |      /       /	                  \     \
>                /	                   \    _| V2
>      _  _  _  / _  _  _  _  _  _  _  _  _  \  _  _  _  _  _  _  _  _
>            o  	                       ^     \
>           '|` 	                ----   |      \
>           / \ 		       |    |  |       \
>          -----------------    |    |  |        \
>                               |    |  |         \
>        --->V1x 	            |  |H         \
>                                    |  |       	   \
>   _            	            |  |            \          |
>  |\            	            |  |             \         |
>    \           	            |  |              \	   \   V V3y
>     \          	            |  |               \    \
>      Al-Aqtza Mousq                |  |      ---> V3x  \    _| V3
>	                            |  |                 \
>	                            |  V                  o
>	          The Wall --->     |                    '|`
>	                            |                    / \
>   H   = 25m ?
>   V1x = ?
>   V1y = ?
>   V2y = V1y
>   V2x = V1x
>   |V2|= |V1|
>   V3x = V2x
>   V3y = ??
>   |V3|= Sqrt(V3x^2+V3y^2) = ??
>
>
>
>
>
>	Good Luck
>		-Nevo
>
>
>-- 
>Nevo Y.	 Hed              nyh@wpi.wpi.edu
>++1-508-754-2491          CS student, Worcester Polytechnic Institute.
>"I like my cigar too, but I take it out of my mouth from time to time" G.Marx