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-----Original Message-----
From: Forum for Physics Educators
[mailto:PHYS-L@lists.nau.edu] On Behalf Of Hugh Haskell
Sent: Friday, October 10, 2003 2:02 PM
To: PHYS-L@lists.nau.edu
Subject: Re: scaling laws
At 13:20 -0400 10/10/03, Robert Cohen wrote:
question of
It doesn't appear to me that this "immediately" answers the
why an elephant's heart doesn't have to beat faster. Don'tyou have to
know something about metabolism? Or am I missing a more "immediate"The smaller mouse has a much higher surface are to volume
connection?
ratio than does the larger elephant, hence the energy
generated within the mouse's body is much more easily
radiated away through the body surface. If both generated
heat at the same rate, either the elephant would fry itself
because it couldn't radiate the energy away as rapidly as
would be necessary, or the mouse would freeze itself
(figuratively) because it couldn't generate energy within the
body as rapidly as its body could radiate it away.
Humans may be a better example, because a baby is more nearly
a scaled down adult than a mouse is a scaled down elephant.
But the size difference isn't as great so the effect won't be
as great. Typical adult heart rates are around 70, while
those of infants are around 110-120. The difference can be
accounted for by the difference in surface to volume ratio
between infants and adults.
There is a nice book on scaling laws in biology called
"Newton Rules Biology," by C. J Pennycuick (Oxford, 1992),
that deals with these issues and more. There are lots of nice
examples of scaling as applied to biological systems in it.
Hugh