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Determining Fatal Injury Collisions
Name: Jon
Status: Student
Grade: 9-12
Location: IL
Country: United States
Date: November 2008
Question:
In a fall from say a 6 story building, there are many
circumstances that will allow someone to survive, with or without injury.
Where would you find this information? I.e. Hitting snow and hitting
cement are completely different variables. They both have different
'spring constants' and thus give a different impact. Based on how you
land, feet first and roll, sideways, feet flat etc. What is the general
formula or maximum capacity of bone structure to resist/sustain injury?
Application: Your only way off the cliff is to jump. Four landings: snow,
water, pine tress, ground. The one thing I know how to predict is the
final velocity.
You can drop say a rock and record the time of fall,
(assuming you are not high enough to create a substantial air resistance,
and neither object reaches terminal velocity in the fall). With this time
you can plug it into the BIG FOUR formulas, and figure out how high you
are, what your final velocity will be etc. How do you figure out a fatal
or injury susceptible height?
Replies:
Your questions include both engineering and anatomy and physiology
considerations. For the engineering considerations the next step in your
analysis would be to understand the nature of the material you were landing
in and how quickly and over what distance you would accelerate from terminal
velocity to zero. For example if you landed on a thick foam cushion and
accelerated from say 88 fps to 0 fps in 0.1 second and sunk in the foam 4.4
feet you could determine the acceleration your body experienced. If I did
my math right that would result in about -880 ft/sec2 or about 28 g's. This
acceleration would then result in forces being applied to the body from the
F=MA relationship This force in turn could be used to determine a stress
(lbs/in2) if you knew how the body landed and what area struck the foam pad.
As you can readily see if you land on something hard that does not compress
the deceleration increases to an extremely high value.
To determine body injury's would be much more complicated and beyond what I
could comment much about. Certain organs would rupture and bones would
break at various g levels from the resultant force. I do not recall exact
values but I believe stunt pilots experience 5 - 10 g's in their maneuvers
without injury. As you go beyond these values and depending on how you
land and what part of the body takes the force I would think you would
expect injury.
Carlton Schroeder
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Update: June 2012
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