Re: T. rex mechanix

[Tom T <tomt@f1.net.au>]

ngear@gvtc.com wrote:
> 
> bettyc@flyinggoat.com wrote:
> >you are basing your assumptions on the ratio of 20 feet ladder x 6 ft
> >height of human---try the ratio of 20 foot ladder and 15 foot tall
> >person.  Suddenly pivots do not look so odd.
> 
> Doubtless someone will already have pointed out that a rex 15 feet tall
> would have been closer to 40 than 20 feet long, but the real problem here is
> that the height of the person (or rex) is irrelevant.  It would take just as
> much time and energy for a 15 foot person to swing a 20 foot ladder as it
> would a 6 or even 3 foot tall person.  What matters is the proportion of
> your plant (the longest dimension of your contact with the ground) to your
> moment (inertia) about the vertical axis.
> 
> You can demonstrate this for yourself by doing the Maytag (not for people
> with back problems; use low heel shoes only).  First plant your feet far
> apart and twist left and right with your arms down at your side and note how
> fast and easily you can do this.  Next try it again placing your feet right
> against each other.  You will notice your pivot speed drops a bit and your
> feet
>  will try to slip more.  Keeping your feet together, extend your arms
> out sideways and see how fast you can twist.  Slower still, right?  Next try
> it holding weights out at arms length (gallon milk or water bottles work
> pretty well).  By this point you will probably be down to a fraction of your
> original twist speed and ground friction is becoming a serious
> consideration.  (And you are still a long way from having a beam that
> reached nearly 40 feet in length weighing something like six tons or more.)
Don't try this with a full stomach, folks.  Trust me.  It's not a
pleasant experience.
> 
> 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.
> 
> Nicholas Wren
Tom