Re: Flying birds

Date:         04 Jun 99 00:59:37 
From: (ref)
Organization: Real/Time Communications - Bob Gustwick and Associates
References:   1 2
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In article <>,
Steve Lacker  <no@spam.thanks> wrote:
>John Gunnar Enebak wrote:
>> You fill a cargo plane with 20 tons of birds, and fly 500 knots at
>> 10.000 feet with the birds sitting on the floor of the plane.
>> Suddenly all the birds start flying around inside the plane. Will the
>> plane then loose 20 tons of weight and start a climb?
>What a funny mental image.... ;-)
>The answer is "no".
>The plane, the air it holds, and the birds within constitute a "closed"

Open or closed, it doesn't matter. When the birds are flying, they're
not attached to the mass of the airplane in any way.

Suppose you're looking at a boat. Its weight causes it to sit X inches
into the water. Now see 100 lbs. of birds flying over it, hovering
just off the boat's deck. Would it sink deeper into the water? No, of
course not.

Now suppose a big hatch closed over the boat and the birds, still hovering,
were now enclosed under the cover. Would the boat suddenly become
"heavier" and sit deeper into the water? Of course not.

Same thing with the birds in the plane.

Ron M.