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Author Topic:   Counter-Intuitive Science
Minnemooseus
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Posts: 3941
From: Duluth, Minnesota, U.S. (West end of Lake Superior)
Joined: 11-11-2001
Member Rating: 10.0


Message 59 of 182 (600145)
01-12-2011 8:40 PM
Reply to: Message 53 by lyx2no
01-12-2011 11:21 AM


Re: Balloons
That the pressure on the inside of a hot air balloon is the same as the pressure outside the balloon.
OK, I'm calling you on this one.
The inside and outside pressures are equal at the bottom of the balloon IF the heating burner is not running. While the burner is running, the pressure inside will be (slightly) higher.
Regardless, at the top of the balloon the inside pressure is higher than the outside pressure.
Moose

This message is a reply to:
 Message 53 by lyx2no, posted 01-12-2011 11:21 AM lyx2no has not replied

Replies to this message:
 Message 60 by jar, posted 01-12-2011 8:47 PM Minnemooseus has replied

  
Minnemooseus
Member
Posts: 3941
From: Duluth, Minnesota, U.S. (West end of Lake Superior)
Joined: 11-11-2001
Member Rating: 10.0


Message 61 of 182 (600150)
01-12-2011 9:29 PM
Reply to: Message 60 by jar
01-12-2011 8:47 PM


Re: Balloons & Bubbles
Is the pressure inside a bubble greater than outside the bubble?
I think yes, albeit only slightly. For a latex party balloon the interior pressure would be more different.
Note, however, that lyx2no is talking about a hot air balloon, one that is not closed off at the bottom.
Moose

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 Message 60 by jar, posted 01-12-2011 8:47 PM jar has replied

Replies to this message:
 Message 62 by jar, posted 01-12-2011 9:31 PM Minnemooseus has replied

  
Minnemooseus
Member
Posts: 3941
From: Duluth, Minnesota, U.S. (West end of Lake Superior)
Joined: 11-11-2001
Member Rating: 10.0


Message 70 of 182 (600162)
01-12-2011 10:50 PM
Reply to: Message 62 by jar
01-12-2011 9:31 PM


Re: Hot air balloons
Is the issue pressure or density? Why would the pressure be higher at one point then another?
The following assumes the burner is not operating, and it hasn't been recently operating. Temperature, pressure, and density gradients are at equilibrium.
My image is that the interior and exterior temperature, pressure, and density are the same at the bottom. There is no physical barrier to separate interior from exterior, and they are at equilibrium.
At the balloon top, the air is at its highest temperature, highest pressure, and lowest density. The higher T dominates over the higher P, and thus the lower density.
The pressure/height in the balloon analogy would be an inverted pressure/depth in water situation. Greater height results in greater pressure like greater depth results in greater pressure.
No, I don't have the physics to back this up, and I'm not going to pursue such. I have nothing further to say beyond "I may be wrong" - Let a real physicist take it from here.
Moose
Added by edit (Gas laws):
Boyle's law - Wikipedia
Charles's law - Wikipedia
Edited by Minnemooseus, : See above.

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