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Footstep sounds - was RE: Novas, Age of Dinos in S.A., pg 203 figure D



> =A0 But they do actually cause vibrations on the ground. Not only are these=
>  distinct=2C they are noticeable for quite a distance.=A0 The concept of tr=
> acking animals by placing your ear to the ground is not fiction=2C for exam=
> ple=2C and despite not impacting the ground=2C a train is capable of produc=
> ing enough force acting on the ground to cause it to vibrate for a very lon=
> g distance so that it can also be "tracked."=A0 Unless you think this is al=
> so fiction.


I think this is due to air actually being a lousy
sound-conductor. here is a nice experiment which was really an
eye-opener for me: Take a very long piece (10 m or so) of wood (I did this in a
kid's park with a tree trunk where this was an experimental setup),
preferredly one that is only supported at a few points.
Put your ear very close to one end of the trunk. Have someone else
scratch the other end with their fingernails slightly, so that they
themselves can just barely hear their own sound. You will hear the
noise clearly at your end.

One other thing to consider here: The sound also depends on how strong
the impact is: elephants, with very soft and big feet, make almost no
sound walking on hard ground, whereas horses do, because the
deceleration of the foot is spread over a longer time. Furthermore,
the pressure below an elephant foot is smaller than that below a horse
hoof (didn't do the calculation, but considering the difference in foot
size this should be obvious.) So with a very big sauropod foot which
may be padded from below there will be not much noise produced (or,
more precisely, the sound produced will be spread over longer time so
that the peak sound amplitude is smaller). 

Cheers,

Martin.


                   Priv.-Doz. Dr. Martin BÃker
                   Institut fÃr Werkstoffe
                   Technische UniversitÃt Braunschweig
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                   e-mail <martin.baeker@tu-bs.de>