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Helium versus vacuum

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imspartacus

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Another silly question:<br /><br />Why is it that Helium/Hydrogen rise--in the air, but a vacuum or near vacuum of the same volume doesn't?<br /><br />What does it technically mean to be 'less dense' in the context of oxygen/helium/vacuum?<br /><br />
 
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heyscottie

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Well, a vacuum of the same volume would rise. Perhaps the reason you think it doesn't is because to keep a hard vacuum, we need strong, heavy walls to stop the implosion and air leakage. So the overall aparatus is denser than the surrounding air.<br /><br />Density is the same no matter what we are talking about -- it is always measured in mass/vol, or in SI units, kg / (m^3).<br /><br />Welcome to SDC!
 
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MeteorWayne

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It is less dense than the surounding material (air) down here so it floats (rises).<br /><br />Once you take that same parcel into the near vaccuum of near space, it is no longer less dense, but more dense, so it sinks and disappates. <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>
 
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