Does warm air rise or does cold air sink?

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Discussion Overview

The discussion revolves around the behavior of warm and cold air, specifically whether warm air rises and cold air sinks. Participants explore this concept through various perspectives, including theoretical explanations, experimental considerations, and analogies.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants assert that warm air rises because it is less dense than cooler air, while cold air sinks when placed in warmer air.
  • Others propose that both phenomena occur simultaneously, with rising warm air displacing cold air downwards.
  • A participant introduces the Rayleigh-Taylor Instability as a relevant concept and mentions conditions under which cold air can remain stable above warm air.
  • One participant questions the analogy of a seesaw to illustrate the dynamics of heavy and light masses, suggesting a need for clarity in understanding the interactions.
  • A participant seeks experimental methods to differentiate between the two propositions regarding air movement.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between warm and cold air, with some emphasizing the simultaneous occurrence of both rising and sinking, while others focus on the individual behaviors of warm and cold air. The discussion remains unresolved regarding the clarity of these interactions.

Contextual Notes

There are limitations in the discussion, including assumptions about density and temperature gradients, as well as the need for clearer definitions of terms like "rise" and "sink." The implications of the Rayleigh-Taylor Instability are also not fully explored.

Who May Find This Useful

This discussion may be of interest to individuals exploring concepts in thermodynamics, fluid dynamics, or atmospheric science, as well as those curious about experimental physics.

somega
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I have a friend and he complained that at school they are teaching that warm air rises.
He said it's wrong. He said instead the cold air sinks.

Is this true?
 
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What is the difference? What sort of experiment could be used to determine the difference between the two propositions
 
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Two ways of saying the same thing, really.
 
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Place a mass of air in air that is cooler and it rises. That is why a hot air balloon rises. Warmer air is less dense than cooler air. Conversely a mass of cool air will sink if place in air that is warmer. This is easily experienced when you open a refrigerator and feel the cool air on your legs first.
 
Both things happen at the same time. If you have some hot air rising, it is displacing cold air which has nowhere else to go but down. So hot air rising is always accompanied by cold air sinking.
 
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It's the Rayleigh-Taylor Instability. Here is a visualization:



Edit: Just for the sake of completeness: A configuration of cold air on top of warm air can be stable if the temperature gradient doesn’t exceed the adiabatic lapse rate. The best example is the atmosphere.
 
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Does the heavy person at one end of a see saw sink or does the light person at the other end rise?
 
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