Why does certain materials flow away from gravity

Discussion in 'Earth Science' started by digitalabstract, Mar 1, 2004.

  1. digitalabstract Registered Member

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    What makes water vapor, smoke, and other materials float away from gravity? I've heard that the materials are so light that they escape gravity but what pushes them into the sky? It seems like if something would escape gravity it would remain in one place.

    Example: Water vapor escapes gravity until it hits the atmosphere then suddenly stops. What is pushing the water vapor up, and why does it stop after it reaches a certain point.
     
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  3. curioucity Unbelievable and odd Registered Senior Member

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    hi & welcome, digital, nice to see you in sciforums.

    As for your question, it's not that those materials are capable of escaping earth's gravity, no. Most of the time, they go further up because of the presence of density difference (think about water and oil, oil can never go beneath the water no matter what you do normally, there amy be some way indeed). Maybe my general explanation is bad, so I'll give you some details (I may miss some here, since I'm not sure about those):
    smoke: they are brought up by hot air (remember that for most materials, the hotter they are the less density they have), say like, when you lit a campfire, the air right above the fire will become so hot that they'll float up, taking any light enough materials with them (and at this stage, the cooler air around the fire will be 'sucked' into the fire, go hot and float up too, and the process repeats).
    baloons: hydrogen and helium are two very light gas, in fact, they are the two lightest gas in universe (so far), and even less dense than normal air. Because of that, whether or not they are incased in light enough material, they will fly up.

    I'm not too sure about vapor though..... if I say that heated water will produce vapor which floats up, I'm afraid that will contradict the fact that even in hot days, there may be water vapor (except in ultra dry place like deserts).

    Hope that helps.
     
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  5. spidergoat Valued Senior Member

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    Gravity is a relatively weak force. Capillary action can overcome it easily. Buoyancy, or, the upward force that a fluid exerts on an object less dense than itself, accounts for these instances of rising against gravity.
     
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  7. Starthane Xyzth returns occasionally... Valued Senior Member

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    The rise of heated water vapour, hydrogen or helium in air is purely due to relative buoyancy: they are lighter than the surrounding medium, so it moves beneath them and pushes them upward. It's the same as bubbles of air rising through water, or lighter granitic materials moving upward through granite and peridotite in the Earth's upper mantle.

    The collection of oil on the surface of water in a saucepan is, in fact, a simplified model of how the interiors of planets differentiate!
     
  8. curioucity Unbelievable and odd Registered Senior Member

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    looks like I'm the only one left behind here eh......
     
  9. John Connellan Valued Senior Member

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    Most things never escape gravity really. All those things u mentioned rise bacause they are being carried upwards by warm air currents. Warm air rises because the cold air 'pushes' it up (more dense). When warm air becomes cold again it sinks. Hydrogen also rises due to pushing of dense air but not because its warm so it keeps rising until it reaches the top layer of the atmosphere. Most of the hydrogen from earth has actually been lost completely because it has been blown away or recieved energy from the sun which allowed it to escape the extremely weak clutches of gravity at this height.
     
  10. Starthane Xyzth returns occasionally... Valued Senior Member

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    One wonders how much mass the Earth has lost in the form of escaping hydrogen. (Probably nowhere near as much as it gains from continuing meteoric accretion).
     
  11. John Connellan Valued Senior Member

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    I worked out an estimate and it comes to about 0.000000265 % of the mass of the earth which is quite tiny. This also assumes the concentration of H in the atmosphere was half the concentration at which it becomes highly flammable (which is probably too much anyway).
    The other thing to remember is that a lot of the H did not escape but went into common molecules with Carbon and Oxygen.
     

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