Hot air balloon thermodynamics

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Discussion Overview

The discussion revolves around the thermodynamics of hot air balloons, specifically addressing how the pressure, volume, and temperature of the air inside the balloon interact as it is heated. The scope includes conceptual understanding and exploratory reasoning regarding gas behavior in the context of buoyancy.

Discussion Character

  • Exploratory, Conceptual clarification, Debate/contested

Main Points Raised

  • One participant suggests that the number of air molecules decreases when the balloon is heated, leading to a decrease in density while keeping pressure constant due to increased kinetic energy of the remaining molecules.
  • Another participant questions the assumption that the volume of the balloon remains constant when heated, implying that the balloon expands.
  • A third participant asserts that while the volume is constant, the heating of the air reduces its density compared to the cooler surrounding atmosphere, contributing to the buoyancy effect.
  • A later reply supports the idea that heating the air results in a reduction of the number of molecules inside the balloon.

Areas of Agreement / Disagreement

Participants express differing views on whether the volume of the balloon remains constant during heating, leading to a lack of consensus on this aspect of the discussion.

Contextual Notes

There are unresolved assumptions regarding the behavior of gas under heating conditions, particularly concerning the relationship between pressure, volume, and temperature in the context of buoyancy.

gersetaffe
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In hot air balloons the air inside the envelope stays at atmospheric pressure because of the hole in the bottom and the volume of the envelope is essentially constant. Yet in order to raise the balloon it must be heated which increases the its temperature. If the temperature increases how does the pressure and volume stay constant?

My guess is that the number of molecules of air in the balloon decreases (decreasing the density). The pressure stays the same because the increased temperature increases the kinetic energy of the remaining molecules.

What do you think? I'm not sure if my guess is correct.
 
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What makes you think the volume is constant? When you heat the air the balloon gets bigger.
 
Volume within the balloon is constant, but due to the higher temperature, the density is less inside the balloon than the surrounding cooler atmosphere, resulting in bouyancy effect.
 
...so yes when you heat the air you reduce the number of molecules in the balloon.
 

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