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Path: utzoo!watmath!watnot!watdcsu!dmcanzi
From: dmcanzi@watdcsu.UUCP (David Canzi)
Newsgroups: net.origins
Subject: Re: Those amazing 250 pound birds.
Message-ID: <1626@watdcsu.UUCP>
Date: Thu, 22-Aug-85 22:34:12 EDT
Article-I.D.: watdcsu.1626
Posted: Thu Aug 22 22:34:12 1985
Date-Received: Sat, 24-Aug-85 15:50:02 EDT
References: <1600@watdcsu.UUCP> <417@baylor.UUCP>
Reply-To: dmcanzi@watdcsu.UUCP (David Canzi)
Distribution: net
Organization: U of Waterloo, Ontario
Lines: 54
Summary: 

In article <417@baylor.UUCP> peter@baylor.UUCP (Peter da Silva) writes:
>> Sure, the bird would weigh less, but so would the air.  The lighter air
>> would, as a result have lower pressure, and as a direct result lower
>> density.  Even though the bird would be lighter, the thinner air still
>> wouldn't be able to support it.
>
>The limiting factor in bird growth isn't wing size, it's muscle power. A
>bird of indefinit seize can glide. The problem is moving the wings: pushing
>a mass of air around.
>
>Even if the gravity and air pressure are less, the bird can still generate
>the same amount of power & would be able to fly.

If the bird simply glided, it would have the same glide slope under
heavy gravity as it would under light gravity (since the density of the
air will be proportional to the strength of gravity).  I expect a bird
with 15 foot wings would tend to avoid flapping them.  It could search
out updrafts and circle in them to gain altitude, as needed.

If it's too far to the nearest updraft, the bird may *have* to flap its
wings.  Under lighter gravity, the bird has less energy because it's
breathing thinner air.  It maintains altitude by accelerating some mass
of air downwards, but under lighter gravity, less mass must be
accelerated downwards, so less energy is required.  So far, the
advantages and disadvantages of lighter gravity balance.

In order to accelerate this smaller mass of air downwards, the bird
must flap its wings at the same rate as it would in heavier gravity,
because the air is thinner.  The effort required to flap its wings, ie.
to accelerate the mass of its wings upward at the end of the downstroke
and downward at the end of the upstroke, remains the same for our poor
oxygen-starved bird.  This means (if I've managed to take everything
into account -- I doubt it) that under lighter gravity, it would
actually be harder for the bird to fly.

So, if the pteratorn couldn't fly today, it would have had to walk
back then too.

>Of course there are still many problems with the "low gravity" thesis. Here's
>one:
>
>	If skylab came crashing down in a couple of years, how long
>	would the aqueous firmament stay up?

If the orbiting water is far enough above the atmosphere, this would
not be a problem.  The water would have to be orbiting either as a ring
around the earth, or as a spherical body like the moon (held together
against tidal forces by surface tension, perhaps?)  I'd be interested
(and probably amused) to find out what shape Velikovsky thought the
mass of water took.

We shouldn't be arguing... we're on the same side... I think...
-- 
David Canzi