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Author Topic: How do gravity and buoyancy relate?  (Read 4788 times)

Offline gazza711

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How do gravity and buoyancy relate?
« on: 08/11/2014 19:29:05 »
wow.Thats so kool what replies I got.Its all in the SUBJECT words.I too believe that we are pushed to the earth,not pulled.what are your thoughts anyone?


 

Offline chiralSPO

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Re: How do gravity and buoyancy relate?
« Reply #1 on: 08/11/2014 19:47:14 »
wow.Thats so kool what replies I got.Its all in the SUBJECT words.I too believe that we are pushed to the earth,not pulled.what are your thoughts anyone?


If gravity is a push-type force, why does it depend so much on the masses of the bodies involved? The force of gravity exerted by the Earth on my body is much more than the force that would be exerted by Mars, if I were on the surface of Mars. If it were something from outside pushing down, presumably the forces would be essentially the same since the "outside" of Earth is essentially the same as the "outside" of Mars.
« Last Edit: 13/06/2015 16:15:56 by chiralSPO »
 

Offline gazza711

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Re: How do gravity and buoyancy relate?
« Reply #2 on: 08/11/2014 20:06:42 »
Uhuh.I like people like you.Im eager to discuss this.

Why does the moon keep us on its surface?Same reason as mars situation.But were still attracted somehow.The force exerted is earths atmosphere,not earth itself.So on mars,there is a small atmosphere-just like on the moon-yes,the moon has a sodium atmosphere.Why is there more pressure the deeper we go in water.Its buoyancy that's keeps all that we see pushed to the ground like a helium balloon is pushed to ur ceiling in ur living room.

Have I lost you yet?

If a feather and bowling ball were dropped at the same time in a near perfect vacuum,99.99999% vacuum,the objects fall extremely slowly towards the ground.why.The other .001111111% gases are doing the pushing on the objects maybe.Gallileo experiment.

Thanks for ur response dude.
 

Offline gazza711

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Re: How do gravity and buoyancy relate?
« Reply #3 on: 08/11/2014 21:41:43 »
why would it depend so much on the masses of the bodies involved?
 

Offline chiralSPO

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Re: How do gravity and buoyancy relate?
« Reply #4 on: 13/06/2015 16:31:09 »

the moon has a sodium atmosphere.

No it doesn't. Where did you get this (mis)information? The moon does have an atmosphere, but the pressure is about 3x10–15 times the pressure on Earth 99.999999999997% vacuum compared to Earth's atmosphere. Mostly it is made of helium, neon and hydrogen.

Why is there more pressure the deeper we go in water.Its buoyancy that's keeps all that we see pushed to the ground like a helium balloon is pushed to ur ceiling in ur living room.

There is more pressure under deep water because there is more water above you, and all of it is being pulled down by gravity.

Buoyancy has to do with relative densities in a gravitational field. If the helium balloon has less mass than an equal volume of the air around it, the air around it will fall as it rises. This process will continue until the balloon reaches a point where the air around it has the same density, or until the balloon bursts.


If a feather and bowling ball were dropped at the same time in a near perfect vacuum,99.99999% vacuum,the objects fall extremely slowly towards the ground.why.The other .001111111% gases are doing the pushing on the objects maybe.Gallileo experiment.

No. The Gallileo experiment has been performed in near perfect vacuum, and the objects fall faster in vacuum than in air.

(note the vacuum drop starts at about 2:50, and is shown in slow motion, this is not how fast they actually fell; also shown at 4:15)
 

Offline evan_au

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Re: How do gravity and buoyancy relate?
« Reply #5 on: 15/06/2015 22:25:52 »
I think the hypothesis here is backwards:
  • It is proposed that atmospheric pressure causes gravity
  • When in fact gravity causes atmospheric pressure 

Atmospheric pressure is caused by gravity, but it is a very non-linear relationship, since
  • a very light body (like the Moon) will lose virtually all its atmosphere
  • while a heavier body (like the rocky core of Jupiter) will retain almost all its atmosphere, including hydrogen & helium
  • So this hypothesis badly underestimates the gravity on the Moon, and overestimates the gravity on Jupiter

Atmospheric pressure is also affected by multiple other factors, like:
  • Strength of the Solar Wind: This is very strong near Mercury, and much weaker out past Jupiter. The solar wind can tear away at the upper atmosphere.
  • Strength of the planetary magnetic field: A strong magnetic field (like Earth or Jupiter) tends to deflect the more energetic outbursts of the solar wind around the planet.
  • Temperature: A hot planet like Venus will drive all liquids and gases into the atmosphere, producing an enormous atmospheric pressure. On the other hand, on Mars, liquid water is frozen out under the surface, producing a very low atmospheric pressure. However, the surface gravity of both bodies is similar.
  • History: The position in the solar system where the planet formed, which determines how it reached its current mass. The orbits of planets in the Solar System does change over astronomical time periods.

So any relationship between atmospheric pressure and gravity is very indirect, with lots of confounding factors.
 
However, as Newton showed, mass causes gravity, and there is quite a simple relationship between the mass of the bodies, the distance between them, and the gravitational force of attraction between them.

 

Offline gazza711

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Re: How do gravity and buoyancy relate?
« Reply #6 on: 20/06/2015 07:22:53 »
I think the hypothesis here is backwards:
  • It is proposed that atmospheric pressure causes gravity
  • When in fact gravity causes atmospheric pressure 

Atmospheric pressure is caused by gravity, but it is a very non-linear relationship, since
  • a very light body (like the Moon) will lose virtually all its atmosphere
  • while a heavier body (like the rocky core of Jupiter) will retain almost all its atmosphere, including hydrogen & helium
  • So this hypothesis badly underestimates the gravity on the Moon, and overestimates the gravity on Jupiter

Atmospheric pressure is also affected by multiple other factors, like:
  • Strength of the Solar Wind: This is very strong near Mercury, and much weaker out past Jupiter. The solar wind can tear away at the upper atmosphere.
  • Strength of the planetary magnetic field: A strong magnetic field (like Earth or Jupiter) tends to deflect the more energetic outbursts of the solar wind around the planet.
  • Temperature: A hot planet like Venus will drive all liquids and gases into the atmosphere, producing an enormous atmospheric pressure. On the other hand, on Mars, liquid water is frozen out under the surface, producing a very low atmospheric pressure. However, the surface gravity of both bodies is similar.
  • History: The position in the solar system where the planet formed, which determines how it reached its current mass. The orbits of planets in the Solar System does change over astronomical time periods.

So any relationship between atmospheric pressure and gravity is very indirect, with lots of confounding factors.
 
However, as Newton showed, mass causes gravity, and there is quite a simple relationship between the mass of the bodies, the distance between them, and the gravitational force of attraction between them.
Hi.What are the chances anyones going to answer to a post from 18/11/15.I am very honoured as I thought I was mearly a blip on your radio.
Mars and venus have way different gravity's.
A lot of 'facts' in planetology might involve a lot of assumptions.Cavendish experiment predicted a lot of things.
So if air we breath has a weight(mass),it must have a downward force of some sort?
So a trillion cazillion atoms in the atmosphere with mass can(entrophic idea maybe)exert a force.water is in most things.without the water,most things would break up and disappear.So when we talk about gravities on other planets and moons for example,you might find that temps on most planets cause the gas,liquid and solid formations.when a gas in the atmosphere is cooled-what happens-gravity or density displacement?
A bit like a bucket of sand.The sand is the atmosphere pressurised by the outside vacuum.you are a spec of something at the bottom of that bucket.
With regards to gravities on other planets and moons-I think the atmosphere is cleverer than we think.
The problem I have in all of this as you know is-what modern proof do we have that objects attract?using lead or metal objects to do experiments is biased-I believe.
I believe that you might have an interest in my findings?or just bored to scroll through peoples old posts-HMMMM.Thanks for the reply.Really enjoying ur comments.Thank you
 

Offline gazza711

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Re: How do gravity and buoyancy relate?
« Reply #7 on: 20/06/2015 07:27:10 »
wow.Thats so kool what replies I got.Its all in the SUBJECT words.I too believe that we are pushed to the earth,not pulled.what are your thoughts anyone?


If gravity is a push-type force, why does it depend so much on the masses of the bodies involved? The force of gravity exerted by the Earth on my body is much more than the force that would be exerted by Mars, if I were on the surface of Mars. If it were something from outside pushing down, presumably the forces would be essentially the same since the "outside" of Earth is essentially the same as the "outside" of Mars.
1.well unless you could weigh planets-which we cant-then you cannot assume their mass.
2.thus we cannot say gravity depends on the bodies involved.
3.how can the outside of earth be the same as the outside of mars?
4.if it was,we wouldn't be going on holiday on earth-mars is the same isn't it.cant see that one happening.
 

Offline PmbPhy

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Re: How do gravity and buoyancy relate?
« Reply #8 on: 20/06/2015 12:05:59 »
Quote from: gazza711
wow.Thats so kool what replies I got.Its all in the SUBJECT words.I too believe that we are pushed to the earth,not pulled.what are your thoughts anyone?
I don't think you understand the different between something being pushed or pulled. It really only has meaning for macroscopic objects with a finite length, width and height.

Push - To push something means that a force is exerted on the surface of the body directed into the body. Such a force acting in this way acts to compress the body. So you know something is being pushed if the body is being compressed along its length parallel to the direction of the force.

Pull - A body is being pulled if a force is exerted on the surface of a body directed outward from the inside of the body. Such a force acts to extend the body. There will be a tension in the object under such a force.

You could also drill a hole through the body and insert a rod and then exert a force on the rod. Then some parts of the body will be pushed while other parts will be pulled depending on where the rod is inserted. You could also grasp a rod with your hand and exert a force parallel to the rod's length. The part of the rod above the hand in the direction of the force is being pushed while the other part is being pulled.

Gravity does neither of those since it exerts a force not simply on the surface of the object but on each point of the body at the same time.
 

Offline gazza711

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Re: How do gravity and buoyancy relate?
« Reply #9 on: 20/06/2015 12:52:53 »
Quote from: gazza711
wow.Thats so kool what replies I got.Its all in the SUBJECT words.I too believe that we are pushed to the earth,not pulled.what are your thoughts anyone?
I don't think you understand the different between something being pushed or pulled. It really only has meaning for macroscopic objects with a finite length, width and height.

Push - To push something means that a force is exerted on the surface of the body directed into the body. Such a force acting in this way acts to compress the body. So you know something is being pushed if the body is being compressed along its length parallel to the direction of the force.

Pull - A body is being pulled if a force is exerted on the surface of a body directed outward from the inside of the body. Such a force acts to extend the body. There will be a tension in the object under such a force.

You could also drill a hole through the body and insert a rod and then exert a force on the rod. Then some parts of the body will be pushed while other parts will be pulled depending on where the rod is inserted. You could also grasp a rod with your hand and exert a force parallel to the rod's length. The part of the rod above the hand in the direction of the force is being pushed while the other part is being pulled.

Gravity does neither of those since it exerts a force not simply on the surface of the object but on each point of the body at the same time.
So a balloon submerged deep in water.is it being pulled or pushed to the surface?surely the inside of the balloon is too being affected-as a stone drops in water due to......gravity?
Sure,so if water has the same characteristics as the air we breath,then we are dealing with the same thing at different temperatures.
 

Offline alancalverd

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Re: How do gravity and buoyancy relate?
« Reply #10 on: 20/06/2015 13:21:57 »
Sure,so if water has the same characteristics as the air we breath,then we are dealing with the same thing at different temperatures.

Speak for yourself, but I think most of our correspondents are mammals, not fish.
 

Offline PmbPhy

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Re: How do gravity and buoyancy relate?
« Reply #11 on: 20/06/2015 13:22:56 »
Quote from: gazza711
So a balloon submerged deep in water.is it being pulled or pushed to the surface?
Since neither definition applies it's neither pushed nor pulled, just like gravity.
 

Offline jeffreyH

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Re: How do gravity and buoyancy relate?
« Reply #12 on: 20/06/2015 14:39:34 »
Gazza, PmbPhy told you what the distinction was between gravity and other types of forces. This is a very important point and you should take it on board. Unless you grasp the concept that gravity acts on every part of a body all at once you will be stuck in your incorrect way of viewing things. Forum members such as Alan, PmbPhy, Evan and Chiral, that are bothering to reply to you, know what they are talking about. By all means ask questions but make no assumptions that anything you believe is right simply because it has popped into your head.
 

Offline gazza711

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Re: How do gravity and buoyancy relate?
« Reply #13 on: 20/06/2015 20:22:19 »
Gazza, PmbPhy told you what the distinction was between gravity and other types of forces. This is a very important point and you should take it on board. Unless you grasp the concept that gravity acts on every part of a body all at once you will be stuck in your incorrect way of viewing things. Forum members such as Alan, PmbPhy, Evan and Chiral, that are bothering to reply to you, know what they are talking about. By all means ask questions but make no assumptions that anything you believe is right simply because it has popped into your head.
Really-are you a scientist?
 

Offline gazza711

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Re: How do gravity and buoyancy relate?
« Reply #14 on: 20/06/2015 20:23:29 »
Sure,so if water has the same characteristics as the air we breath,then we are dealing with the same thing at different temperatures.

Speak for yourself, but I think most of our correspondents are mammals, not fish.
and the others?Arent whales mammals?
 

Offline gazza711

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Re: How do gravity and buoyancy relate?
« Reply #15 on: 20/06/2015 20:28:30 »

the moon has a sodium atmosphere.

No it doesn't. Where did you get this (mis)information? The moon does have an atmosphere, but the pressure is about 3x10–15 times the pressure on Earth 99.999999999997% vacuum compared to Earth's atmosphere. Mostly it is made of helium, neon and hydrogen.

Why is there more pressure the deeper we go in water.Its buoyancy that's keeps all that we see pushed to the ground like a helium balloon is pushed to ur ceiling in ur living room.

There is more pressure under deep water because there is more water above you, and all of it is being pulled down by gravity.

Buoyancy has to do with relative densities in a gravitational field. If the helium balloon has less mass than an equal volume of the air around it, the air around it will fall as it rises. This process will continue until the balloon reaches a point where the air around it has the same density, or until the balloon bursts.


If a feather and bowling ball were dropped at the same time in a near perfect vacuum,99.99999% vacuum,the objects fall extremely slowly towards the ground.why.The other .001111111% gases are doing the pushing on the objects maybe.Gallileo experiment.

No. The Gallileo experiment has been performed in near perfect vacuum, and the objects fall faster in vacuum than in air.

(note the vacuum drop starts at about 2:50, and is shown in slow motion, this is not how fast they actually fell; also shown at 4:15)
Yes.I felt a bit of an idiot when I wrote that.I thought I was onto something whilst watching Brian Cox do the Gallileo experiment. Didn't think it through.Was obvious once I pressed the POST button.OOPS
 

Offline PmbPhy

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Re: How do gravity and buoyancy relate?
« Reply #16 on: 20/06/2015 21:18:14 »
Gazza, PmbPhy told you what the distinction was between gravity and other types of forces. This is a very important point and you should take it on board. Unless you grasp the concept that gravity acts on every part of a body all at once you will be stuck in your incorrect way of viewing things. Forum members such as Alan, PmbPhy, Evan and Chiral, that are bothering to reply to you, know what they are talking about. By all means ask questions but make no assumptions that anything you believe is right simply because it has popped into your head.
Really-are you a scientist?
Yes. Among other things, I consider Jeff to be a scientist. Do you actually know what a scientist is? Please look it up.
 

Offline gazza711

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Re: How do gravity and buoyancy relate?
« Reply #17 on: 20/06/2015 22:11:12 »
Gazza, PmbPhy told you what the distinction was between gravity and other types of forces. This is a very important point and you should take it on board. Unless you grasp the concept that gravity acts on every part of a body all at once you will be stuck in your incorrect way of viewing things. Forum members such as Alan, PmbPhy, Evan and Chiral, that are bothering to reply to you, know what they are talking about. By all means ask questions but make no assumptions that anything you believe is right simply because it has popped into your head.
Really-are you a scientist?
Yes. Among other things, I consider Jeff to be a scientist. Do you actually know what a scientist is? Please look it up.
Just asked. I have never made an assumption. I just don't ask in a scientific way. I simply ask-why do you believe all tings attract. Theres more posts on the internet disproving newton and saying GR is far fetched as well. Actually newton disproved many times. they said the world was flat not long before that....So if your a scientist-prove attraction not repulsion(my argument)using more than silly examples like Cavendish and schiehallion.how do we find the mass of planets without formulas,equations etc. astronomy is based on assumptions everyday. The fact is that im stating repulsion and the "CASIMIR EFFECT" looks plausible maybe.
 

Offline alancalverd

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Re: How do gravity and buoyancy relate?
« Reply #18 on: 22/06/2015 23:25:31 »

and the others?Arent whales mammals?

To the best of my knowledge, all whales and all correpondents to this forum, know that water and air do not "have the same characteristics".
 

Offline PmbPhy

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Re: How do gravity and buoyancy relate?
« Reply #19 on: 23/06/2015 04:51:50 »
Quote from: gazza711
Theres more posts on the internet disproving newton and saying GR is far fetched as well. Actually newton disproved many times.
And not one of them by anybody who knows what they're talking about. Only crackpots make those claims. Newton's laws and Einstein's theories have withstood the test of time and their validity have been borne out by experiment countless times. So what you read was absolute total garbage. What else is new?
 

Offline rmolnav

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Re: How do gravity and buoyancy relate?
« Reply #20 on: 24/06/2015 10:42:45 »
Gazza711, #9
You ask:
"So a balloon submerged deep in water.is it being pulled or pushed to the surface?"
Any submerged object experiences water pressure all around its surface. That pressure is due and equal to the weight of a column of water with a surface unit section, and going from water surface to the considered point of the object surface (water pressure PUSHES object surface ...)
Integration of all forces due to that pressure (pressures multiplied by surfaces) gives an upward push. Arquimedes discovered that: net total push is equal to the weight of the liquid previously filling the space where the object is situated.
If that upward push is bigger than object own weight, the push not compensated by object weight will make it move up.
If object weight is bigger (it would mean its average density is higher than water´s), then the object would further sink (not compensated weight would PULL it down: gravity is attraction between massive objects, kind of "tele-pull").   

 
 

Offline PmbPhy

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Re: How do gravity and buoyancy relate?
« Reply #21 on: 24/06/2015 11:27:09 »
Quote from: gazza711
is it being pulled or pushed to the surface?
I can't believe that you asked me this question in reply #9 since I just answered it in reply #8, i.e. the part that you quoted. So why on Earth id you ignore it?

Do you even know what those terms, i.e. push and pull mean?
« Last Edit: 24/06/2015 11:28:40 by PmbPhy »
 

Offline gazza711

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Re: How do gravity and buoyancy relate?
« Reply #22 on: 25/06/2015 14:10:44 »
Quote from: gazza711
is it being pulled or pushed to the surface?
I can't believe that you asked me this question in reply #9 since I just answered it in reply #8, i.e. the part that you quoted. So why on Earth id you ignore it?

Do you even know what those terms, i.e. push and pull mean?
Ok.are attracted or repelled then as the other words are incorrect.dont answer without self evidence.
 

Offline gazza711

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Re: How do gravity and buoyancy relate?
« Reply #23 on: 25/06/2015 14:19:58 »

and the others?Arent whales mammals?

To the best of my knowledge, all whales and all correpondents to this forum, know that water and air do not "have the same characteristics".
Ok.so air and water have similar characteristics.theyre breathable,use convection to help create movement,you could swim in air(drag),water is part oxygen.any suggestions on more similarities?
 

Offline chiralSPO

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Re: How do gravity and buoyancy relate?
« Reply #24 on: 25/06/2015 14:33:24 »

Ok.so air and water have similar characteristics.theyre breathable,use convection to help create movement,you could swim in air(drag),water is part oxygen.any suggestions on more similarities?

Every fluid has drag and can convect. Oxygen is the most common element on Earth (by mass).
You're really grasping at straws here. This is not at all scientific.

Water and air are also both transparent in the visible region (but so is glass, diamond, polycarbonate plastic, hydrofluoric acid, etc. etc. etc.), but that has nothing to do with gravity... Water and air both have mass (so does pretty much all matter), and that does have to do with gravity, but isn't very helpful. Water and air are both fairly nontoxic (you can drink enough water to kill you, enough nitrogen will result in narcosis, coma or death, too much oxygen is neurotoxic and carcinogenic...)
 

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Re: How do gravity and buoyancy relate?
« Reply #24 on: 25/06/2015 14:33:24 »

 

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