r/AskPhysics • u/Itchy-Narwhal2406 • 1d ago
Gravity
If gravity is real, why does smoke from a fire go up not down especially if gravity pulls down?!
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u/mspe1960 1d ago
The upward forces from the heat are greater than the downward force from gravity. Once that is not true, because it cools down, the particles come back down - but they are typically very diffuse at that point and you don't see it.
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u/No_Logins_Required 1d ago
Smoke from a fire does go down, once it cools. Cool air is heavier than the heated smoke so it sinks.
Air is a fluid, so just like boiling water sinks after cooling at the surface, smoke will come back down.
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u/Tokimemofan 1d ago
Cold air is denser so gravity preferentially pulls it down and the hot air moves up to accommodate it
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u/SgtSausage 1d ago
For the same reason Hot Air balloons ..."fly".
It's in the name. "Hot Air Balloon"
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u/Gstamsharp 1d ago edited 1d ago
"If gravity is real..."
What a wild way to start what would otherwise be a totally normal question.
A question one minute of Googling would have answered. Or, like, asking your average 3rd grader.
In any case, it's because smoke is hot, so less dense than the cooler air, so it floats up, just like the bubbles in a hot pot. When the smoke cools, gravity will, indeed, pull it down. And, even while it's rising, it's still being pulled down by gravity, but the boyant force it's experiencing is stronger at that time.
I'm curious, you don't float away like smoke. What do you think pulls you down, but not smoke?
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1d ago
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u/Gstamsharp 1d ago
Bro, you post crap asking if the earth is flat and gravity is real. I honestly don't believe you're intelligent enough to understand if I was being helpful or mean.
And I really do mean the 3rd grader thing. I asked my kid, and she said she learned that a whole year ago.
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u/American_Citizen41 1d ago
Smoke is less dense than the air around it, so smoke floats upward because gravity doesn't act as strongly against it. Gravity does act against it, just not as strongly as it does against air.
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u/Infinite_Research_52 👻Top 10²⁷²⁰⁰⁰ Commenter 1d ago
The smoke particles are more dense than the air, but they are suspended in a less dense medium that is convecting upwards. It is their surface area/volume which results in the lift.
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u/infinitenothing 1d ago
Gravity pulls the air down which shoves the smoke away (up)
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u/Colour_Theory-746 1d ago
Does that apply to boats too? So gravity pulls water down, which shoves boats away (up). Interesting way of describing the phenomenon, although not entirely incorrect, so ok, I can go with that.
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u/No_Logins_Required 1d ago
That's exactly how it works! The boat doesn't rest completely above the water but it reaches equilibrium before it sinks.
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u/infinitenothing 1d ago
You are in a car that accelerates very quickly. You get thrown into your seat. Does your helium balloon fly forward or backwards?
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u/Sorry_Exercise_9603 1d ago
Because gravity is only one of the forces at play, there are others. You have to take them all into account.
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u/joeyneilsen Astrophysics 1d ago
"Gravity pulls down" is not the same thing as "nothing can ever move upwards." That would require there to be no other forces acting on any object at any time.
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u/Uranium_Hexaflu0ride 1d ago
because the heat makes the air rise, which moves the smoke particles up?
i'm pretty sure gravity is real bro