Re: T. rex mechanix

[Bill Adlam <wa105@mead.anglia.ac.uk>]

Nicholas Wren wrote:

>You can demonstrate this for yourself by doing the Maytag...
>
>While it is true the rex foot was bigger than ours it was still a small
>fraction of the rex's effective body length, and I think this is the
>proportion we need to focus on.

This whole analysis only applies to standing creatures.  When running or 
even walking, it is easy to turn by stepping slightly differently.  If the 
force you exert on the ground (and therefore the force the ground exerts on 
you) does not act through your centre of mass, you will experience a moment 
or torque.

This moment has a component of swaying to one side and a component of 
twisting.  We usually compensate for the slight twisting which occurs 
normally by swinging our arms in antiphase to the ispsolateral legs.  T. 
rex could not do this, and probably moved its neck to mimimise the effects 
on vision.

The important factor in T. rex's manoeuvrability is how far apart its feet 
could tread while running.  I know the feet would normally have been very 
close together, but how far could it have widened the gap without losing 
too much speed?

I can briefly spread my feet about half a metre to make a sharp turn.  I 
would guesstimate (based on distances, moments of inertia and personal 
prejudices) that a 12m-long Tyrannosaurus would have to open its legs to 
about 4m to turn equally fast.  

If I'm on the right track (so to speak), I could work this out a bit more 
seriously, with detailed calculations and experiments on running humans.

                                                        All the best,

                                                                        Bill