Re: Biomechanics

["Martin Barnett" <martin.barnett3@virgin.net>]

----- Original Message -----
From: Ralph W. Miller III <gbabcock@best.com>
To: <dinosaur@usc.edu>
Cc: <dinosaur@usc.edu>
Sent: Monday, September 06, 1999 4:16 PM
Subject: Biomechanics


> Two questions for the engineers in the crowd...
>
> First, what figure would you put on the pressure at the level of the lungs
of a
> large, submerged, snorkeling _Brachiosaurus_ individual with the lungs
about 20
> feet (a tad over 6 meters) below the water level?  Can this be put in
terms of psi
> (pounds per square inch)?  I'd appreciate seeing how you arrived at this,
and no,
> you're not doing my homework.  I'm not enrolled in school at this time.  I
> understand that the water pressure would be too much to enable the lungs
and air
> sacs to expand, but I would like to see the predicament quantified.
>
> Second, it has been stated recently on this list that a fast running
_Tyrannosaurus
> rex_ individual (was it 20 meters per second?) would trip and fall on its
skull
> with the force of a bus impacting a brick wall at approximately 60 mph.  I
> understand such a hypothetical tyrannosaur was calculated to have
sustained fatal
> injuries.  My question: is the 60 mph bus analogy apt?
>
> -- Ralph W. Miller III       gbabcock@best.com
>
>


Hi,
I only have an answer for your second question.  For the first you will have
to rely on other list members who, as I see have responded, alternatively,
read The Dynamics of Dinosaurs by R McNeill Alexander for a full chapter on
the matter.  Anyway, back to the second question.  The chap on the list who
suggested the tyrannosaur running at 45 - 50kph (not under any circumstances
could T-rex have hit 20mps unless he was thrown from the fallout of an
asteroid impact, but I won't get into that tired old debate now) estimated a
mass of 6 tonnes when he made the bus analogy.  The tonnage estimated by the
experts who believe he (T-rex) ran that fast is closer to 4 or 5 tonnes,
therefore the bus analogy made by the list member is off a little to start
with unless you convert the bus to a single decker and/or remove some of the
passengers until it is right again(though there was no mention in the
analogy of how many passengers were on this hypothetical bus in the first
place.  Now, secondly, you can't expect a tyrannosaur (90% water if obeying
the same ratios as other contemporary animals which we must assume it does)
to obey the same impact principles as a rigid rectangular immobile metal
object like a bus.  The damage incurred by a bus is bound to be far greater
than anything with even the most remotely flexible spine, not to mention all
the elasticated tendons and shock absorbant flesh rippling on impact.  The
bus is going to crunch along it's geometric metal lines of stress etc... and
be a complete right off whereas a T-rex, despite being the same mass
(hopefully) is going to dissipate that stress throughout it's body (perhaps
a little more stress on the harder fibres such as bone tissue and I don't
know what the thinking is on dinosaurian bone marrow but if it is there it
will also help absorb the impact.  From an engineering point of view, a bus
would not seem to be the best comparison for a crash test series of
experiments in the lab.
Hope this helps,
                         Samuel Barnett