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SpecialistMichael, MS, CSCS
Category: General
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Experience:  Senior Information Specialist
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If gravity takes things down, then why does smoke go upwards?

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If gravity takes things down, then why does smoke go upwards? Is it because of the heat?
My name isXXXXX you for the great question.

Actually the reason smoke rises(assuming it instantly cools off) is because of its density which is less than the air. Normally the air is primarily nitrogen(2 molecules together as n2) but then obviously with some oxygen and a few other things including co2 carbon dioxide.

So to make this easy to understand the double nitrogen has a higher molecular mass than the smoke which we know is carbon MONoxide and some dioxide and then a few other things. Due to the differences in molecular weight(mass) the smoke molecules weigh less than the heavier nitrogen and more important have less mass per unit of space - so they float and want to sit on top of the heavier air.

Similar to why ice floats in water - ice, despite taking up more space has less mass per amoun of space than water so it floats!

So its density mass divided by volume which is the reason things float and separate:)

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sIf we wanted to get super detailed - adding heat would excite the molecules thus changing its density so if we super heated the nitrogen hot enough and kept the smoke cooled, we could get the nitrogen to sit on the smoke. But again at room temp, thats why smoke floats in the air