Why does smoke always rise upwards?

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Discussion Overview

The discussion revolves around the phenomenon of smoke rising, exploring the reasons behind this behavior in various contexts, including the effects of gravity, air density, and convection currents. Participants examine both theoretical and practical aspects of smoke movement, including scenarios involving vacuum conditions.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant suggests that smoke rises due to a 'projection' from a chimney but later questions this by observing smoke from an essence stick and coal, noting that it can move in various directions.
  • Another participant attributes the rising of smoke to convection currents, similar to why hot air rises.
  • A different viewpoint emphasizes that smoke consists of ash particles carried by hot air, which is less dense than cold air, allowing it to rise, although they note that smoke does not always rise under certain conditions.
  • One participant challenges the idea of burning in a vacuum, stating that without oxygen, combustion cannot occur, and suggests that vapors from substances containing their own oxygen would not necessarily rise.
  • Another participant agrees with the idea of smoke heating the surrounding air, creating a draught that carries the smoke, and mentions that the draught may not always lead vertically upward.
  • There is a reiteration of the vacuum scenario, questioning its practicality and suggesting that anything would fill a vacuum regardless of smoke behavior.

Areas of Agreement / Disagreement

Participants express differing views on the mechanics of smoke rising, with some agreeing on the role of convection currents and hot air, while others point out exceptions and challenge the feasibility of certain scenarios, such as burning in a vacuum. The discussion remains unresolved regarding the implications of these ideas.

Contextual Notes

Some assumptions about the behavior of smoke in different environments, such as vacuum conditions, are not fully explored. The discussion also reflects varying interpretations of the density of smoke relative to air and the conditions under which smoke may not rise.

rohanprabhu
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First i thought that smoke used to rise upwards due to a 'projection' created by a chimney.. but lately when I was looking at an essence stick.. the smoke could literally go anywhere. Even the same with a burning piece of coal. Even the smoke generated at the bottom part of the coal 'envelopes' around the piece of coal and rises upwards.

No matter what orientation we select, the smoke always rises upwards. By 'upwards' I mean 'opposite and along the line of force of gravity'.

So.. what exactly is the reason of this happening? My best guess is that this is due to another fluid surrounding the burning object as well as acting as a medium for the travel of smoke [i.e. air]. So.. if i burn a piece of coal in vacuum [just believe that for know we have some oxygen bubbles in the coal itself or something].. will the smoke move around in all directions despite the effect of gravity?
 
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Smoke rises for the same reason 'hot air' rises, convection currents.

Nice Avatar by the way :wink:
 
"Smoke", strictly speaking, consists of particles of ash carried on the hot are from burning. Since hot air is less dense than cold air, it rises as it is displaced by the heavier cold air. I suppose you could say that the "fluid" you are talking about is the cold air. Actually, with the particles of ash, the density is not a great deal less than that of cold air- smoke does not always rise. Depending on the circumstances, it can stay close to the ground.

You cannot have ordinary burning in vacuum- no oxygen. If you were to use a substance that contained its own oxygen, say sodium peroxide, the vapors that came off in vacuum would not rise.
 
rohanprabhu said:
My best guess is that this is due to another fluid surrounding the burning object as well as acting as a medium for the travel of smoke [i.e. air]. So.. if i burn a piece of coal in vacuum [just believe that for know we have some oxygen bubbles in the coal itself or something].. will the smoke move around in all directions despite the effect of gravity?

Hi rohanprabhu! :smile:

I think you're right - the smoke heats the air, and then the hot air rises, causing a draught, which carries the smoke with it. :smile:

The draught will seek out the nearest suitable opening, whch is not necessarily vertically upward … so if you have no chimney, but just make a small hole in the roof, the smoke from a fire should head straight for the hole, instead of filling the room.

I don't think your vacuum suggstion would be very helpful, though - wouldn't anything automatically fill the vacuum?
 
Last edited:
thanks to everybody.. that cleared it up for me.. thanks a lot to HallsOfIvy...

Hootenanny said:
Nice Avatar by the way :wink:

totally.. :D
 

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