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Post by Progenitor A on Sept 30, 2012 9:30:03 GMT 1
Does gravity not act upon helium?
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Post by buckleymanor1 on Sept 30, 2012 11:59:15 GMT 1
Yes gravity does, they go up because air being more dense goes down.Similar to oil floating on the top of water, the oil does not defy gravity it just floats to the top by the action of the more dense water.
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Post by Progenitor A on Sept 30, 2012 14:02:42 GMT 1
Yes gravity does, they go up because air being more dense goes down.Similar to oil floating on the top of water, the oil does not defy gravity it just floats to the top by the action of the more dense water. But the more dense air is equally distributed around the ballon isn't it? So what pressures are forcing the ballon up?
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Post by marchesarosa on Sept 30, 2012 15:48:57 GMT 1
Adiabatic ones?
I learned that word on climate boards. No idea what it means!
There's convection, too.
Gravity is a VERY weak force, anyway, isn't it? Our atmosphere is escaping into space all the time, isn't it, though not at an inconveniently fast rate!
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Post by buckleymanor1 on Sept 30, 2012 19:20:03 GMT 1
Yes gravity does, they go up because air being more dense goes down.Similar to oil floating on the top of water, the oil does not defy gravity it just floats to the top by the action of the more dense water. But the more dense air is equally distributed around the ballon isn't it? So what pressures are forcing the ballon up? I am not sure what you mean by this,just because the more dense air is equally distributed it does not make it any less dense.The force which causes the balloon to rise is atmospheric pressure. Atmospheric pressure is caused by gravity so gravity pulling down on the more dense air causes the less dense helium to rise.
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Post by fascinating on Sept 30, 2012 19:45:38 GMT 1
How does pulling down the more dense air cause less dense helium to rise? Why doesn't the more dense air bear down on the helium balloon, thrusting it to the ground and crushing it until it reaches the same density as the air?
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Post by Progenitor A on Sept 30, 2012 19:47:44 GMT 1
But the more dense air is equally distributed around the ballon isn't it? So what pressures are forcing the ballon up? I am not sure what you mean by this,just because the more dense air is equally distributed it does not make it any less dense.The force which causes the balloon to rise is atmospheric pressure. Atmospheric pressure is caused by gravity so gravity pulling down on the more dense air causes the less dense helium to rise. But you see the dense air is above and below the balloon exerting an equal pressure top and bottom, so the atmosphere is not causing any pressure or force on the balloon is it? Would the ballon rise from a surface with no atmosphere like the moon? It could be adabiatic but that doen't seem a hot line to follow
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Post by buckleymanor1 on Sept 30, 2012 22:53:08 GMT 1
How does pulling down the more dense air cause less dense helium to rise? Why doesn't the more dense air bear down on the helium balloon, thrusting it to the ground and crushing it until it reaches the same density as the air? There is more mass per volume of space in the air so it causes lesser mass per volume helium to rise above it much the same as a beachball would float on water. The more dense air does not crush the helium balloon because gravity on Earth is not strong enough.
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Post by buckleymanor1 on Sept 30, 2012 23:05:29 GMT 1
I am not sure what you mean by this,just because the more dense air is equally distributed it does not make it any less dense.The force which causes the balloon to rise is atmospheric pressure. Atmospheric pressure is caused by gravity so gravity pulling down on the more dense air causes the less dense helium to rise. But you see the dense air is above and below the balloon exerting an equal pressure top and bottom, so the atmosphere is not causing any pressure or force on the balloon is it? Would the ballon rise from a surface with no atmosphere like the moon? It could be adabiatic but that doen't seem a hot line to follow It is not exerting an equal pressure top and bottom.There is less pressure at the top of a balloon because there is a lesser volume of air at the top than at the bottom. Much the same if you stood in a tank of water which just covered your head. There would be more pressure or weight of water on your feet than your head so you rise. On the Moon the balloon would stay put unless another force other than gravity moved it. Adabiatic would be more to do with thermodynamics.
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Post by marchesarosa on Oct 1, 2012 1:23:11 GMT 1
Adabiatic would be more to do with thermodynamics.
So are you ignoring atmospheric heat transport in this discussion? Why?
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Post by Progenitor A on Oct 1, 2012 7:05:49 GMT 1
But you see the dense air is above and below the balloon exerting an equal pressure top and bottom, so the atmosphere is not causing any pressure or force on the balloon is it? Would the ballon rise from a surface with no atmosphere like the moon? It could be adabiatic but that doen't seem a hot line to follow It is not exerting an equal pressure top and bottom.There is less pressure at the top of a balloon because there is a lesser volume of air at the top than at the bottom. Much the same if you stood in a tank of water which just covered your head. There would be more pressure or weight of water on your feet than your head so you rise. On the Moon the balloon would stay put unless another force other than gravity moved it. Adabiatic would be more to do with thermodynamics. Ah we sem to be getting somewhere! So if I were to make a flat balloon (like a very thin plate) with a thickness of 1 molecule of helium it would not go up?
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Post by fascinating on Oct 1, 2012 8:25:26 GMT 1
If you place a beach ball on water then I can understand why it does not sink, because it is less dense than the water, meaning that the gravity being exerted on it is less than that of the water beneath. However we are considering here a helium balloon which starts at the bottom of the atmosphere, not the top.
If you brought a beach ball to the bottom of the ocean, that would also shoot up to the surface, but I still don't understand why. Think of all the work being done to displace all that water on its journey up. Think of the huge pressure of water at the bottom of the ocean, and yet still the balloon is not crushed against the ocean floor.
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Post by mercury on Oct 1, 2012 10:32:53 GMT 1
"Why Do Helium Balloons Go UP?" - cos they is lighter than air.
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Post by Progenitor A on Oct 1, 2012 14:46:45 GMT 1
"Why Do Helium Balloons Go UP?" - cos they is lighter than air. Thankyou for your contribution Mercury, but this is the Grammar School. Off you go back down the road with you now!
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Post by buckleymanor1 on Oct 1, 2012 17:49:02 GMT 1
Adabiatic would be more to do with thermodynamics. So are you ignoring atmospheric heat transport in this discussion? Why? Because it could be confusing , it's easier to describe the rising of a helium balloon up through the atmosphere using Archimedes principle or mechanics.Atmospheric heat transport does not obviously come into play with regards to a balloon rising.Though I imagine an adiabatic process takes place in as much that the helium's temperature within the balloon would go down as it expanded, though no heat would be lost.
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