i have always wondered this and no one seems to ever know the answer.
you have two pipes.. lets just say for the sake of this question they
are PCV pipe. a tire intake valve for air is attatched to each one and
a gauge to measure the ammount of air in each pipe. you fill one will
LOTS of air.. the other one with little or none.

my question is: does the pipe with the more air float more easily? if
you continued to pump air, does it max out and eventually the air
weighs it down? keep in mind, this is not like a rubber float or
baloon, because the pipes do not expand to become more boyant, only
the air inside them change.

i would immagine helium would affect this differently and make them
float.. but i want to know about normal air.

thanks

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Request for Question Clarification by hedgie-ga on 14 Apr 2005 22:59 PDT

Mike,
       I will answer your question, if you confirm that you
indeed just want an answer.  People sometime are expecting a long
dialog in which researcher would be refuting their theories - that
would not work here.

 You float your pipe on some water surface, and we can assume 'normal
conditions', normal reange of temperature and pressures .. .right?

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Clarification of Question by mike123106-ga on 15 Apr 2005 07:29 PDT

hedgie an answer would be fine. thanks

Mikes

    The  comments did answer the question correctly 

(except for minor details - like spelling 'density' as 'dencety')

 so - to provide a bit more in the paid answer - I will include 
 some links:

This one  illustrates the 'density'

http://www.elmhurst.edu/~chm/vchembook/123Adensitygas.html

  Helium not always lighter then air - it depends on pressure.
  When you double the pressure, your double the density - and therefore
  the weight of the gas in the pipe.  When you replace the air by helium
  (at same pressure - 1 atmosphere) your pipe will float a bit higher.
  
 You increase the pressure about 4 times, 
 and it will match the pipe filled with air (at normal pressure of 1 atm.) 
 You increase the pressure some more, and the pipe will sink a bit more ..

  The behaviour is described by combination of the  Archimedes's law
 http://www.grow.arizona.edu/Grow--GrowResources.php?ResourceId=197 

 and Gas Law 
http://www.cei.net/~dvines/introgas.htm

  The weight of the pipe will be 

  W.pipe=  W.empty + V * k.gas * Pressure

  Where W.empty is weight of 'empty' pipe in air 
 (empty means just with normal air, at normal pressure) 
        V is volume of cavity inside the pipe
        and K.gas depends on the gas (Helium, air, ...)

 Bigger the Weight, the more of the pipe will be submerged.
 Since K.gas is very very small, it may be hardly visible.
 
Hedgie

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Clarification of Answer by hedgie-ga on 16 Apr 2005 04:50 PDT

Correction

 Mikes --> should be Mike,

 Where W.empty is weight of 'empty' pipe in air 
 (empty means just with normal air, at normal pressure) 

should be

 Where W.empty is weight of 'empty' pipe in air 
 (empty means evacuated pipe (not even air inside) 


 sorry about those errors.

Thanks yall :)

The answer is very simple.  The more of anything that you put in the
tube the heavier it gets.  The heavier it gets, the less boyant it
becomes.

boyancy is dependent on dencety (and water tension but that is
insignificant in this problem). Denser things sink and things that are
less dense rise on top so for the pipe to float it must be less dense
than water. Water's density is 1 gram per centimiter cubed. The
formula for density is D=M/V where d=density M=mass and V=volume. The
volume of the pipe is constant but mass is increased as you add air so
densety is also increased. After the point where the pipe's densety
becomes grater than 1 gram per centimetre cubed it will sink.