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Author Topic: How do gravity and buoyancy relate?  (Read 4796 times)

Offline gazza711

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Re: How do gravity and buoyancy relate?
« Reply #25 on: 25/06/2015 14:55:48 »

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...)
Well said.just that it was said they don't have same characteristics.nuthin to do with gravity at all.i know.but surely 7lbs/sq inch of downforce with an atmisphere that is 100k feet high that has mass must contribute to something.and all that in a perfect vacuum of ether or something like that.
 

Offline chiralSPO

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Re: How do gravity and buoyancy relate?
« Reply #26 on: 25/06/2015 15:25:54 »
surely 7lbs/sq inch of downforce with an atmisphere that is 100k feet high that has mass must contribute to something.

But it can also be a 7 lbs per square inch of an up force (or a sideways force). Suction cups (https://en.wikipedia.org/wiki/Suction_cup) can stick to an appropriate surface in any direction as long as there is pressure on them from the outside.
 

Offline PmbPhy

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Re: How do gravity and buoyancy relate?
« Reply #27 on: 25/06/2015 17:34:14 »
Quote from: gazza711
Ok.are attracted or repelled then as the other words are incorrect.dont answer without self evidence.
So, you think that the difference between push and pull is the direction of the force. Suppose that we use the electric force as an example so as to illustrate your point about being pushed and pulled.

Let there be two large sheets of charge parallel to the xz-plane. One has a positive charge density +a2ab7d71a0f07f388ff823293c147d21.gif that passes through the y-axis at y = +d, the other having a negative charge density -a2ab7d71a0f07f388ff823293c147d21.gif that passes through the y-axis at y = -d. There is an electric field in the region -d < y < -d. Place a positively charged particle in the region -d < y < +d. In between the plates there is a uniform electric field directed in the +y direction. Outside the region -d < y < +d the electric field is zero.

Now place a positively charged particle at y = 0. In this instance is the particle pushed or pulled?

Now take away the sheet of positive charge. There is still a uniform electric field in the region -d < y < +d. The only difference being the magnitude of the particle. Is the positive particle at y = 0 being pushed or pulled?

Now put the sheet of positive charge back at y = +d and take away the sheet of negative charge. There is still a uniform electric field in the region -d < y < +d. Again, the only difference being the magnitude of the particle. Is the positive particle at y = 0 being pushed or pulled?
« Last Edit: 26/06/2015 01:48:57 by PmbPhy »
 

Offline gazza711

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Re: How do gravity and buoyancy relate?
« Reply #28 on: 25/06/2015 20:07:14 »
Quote from: gazza711
Ok.are attracted or repelled then as the other words are incorrect.dont answer without self evidence.
So, you think that the difference between push and pull is the direction of the force. Suppose that we use the electric force as an example so as to illustrate your point about being pushed and pulled.

Let there be two large sheets of charge parallel to the xz-plane. One has a positive charge density c75df6eaec1cf182bd5225a82b68eef8.gif that passes through the y-axis at y = +d, the other having a negative charge density 11eab9ef7c71e4c86f6234a09d63c11b.gif that passes through the y-axis at y = -d. There is an electric field in the region -d < y < -d. Place a positively charged particle in the region -d < y < +d. In between the plates there is a uniform electric field directed in the +y direction. Outside the region -d < y < +d the electric field is zero.

Now place a positively charged particle at y = 0. In this instance is the particle pushed or pulled?

Now take away the sheet of positive charge. There is still a uniform electric field in the region -d < y < +d. The only difference being the magnitude of the particle. Is the positive particle at y = 0 being pushed or pulled?


Now put the sheet of positive charge back at y = +d and take away the sheet of negative charge. There is still a uniform electric field in the region -d < y < +d. Again, the only difference being the magnitude of the particle. Is the positive particle at y = 0 being pushed or pulled?
I'm done with the push/pull convo.
 

Offline gazza711

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Re: How do gravity and buoyancy relate?
« Reply #29 on: 25/06/2015 20:19:22 »
surely 7lbs/sq inch of downforce with an atmisphere that is 100k feet high that has mass must contribute to something.

But it can also be a 7 lbs per square inch of an up force (or a sideways force). Suction cups (https://en.wikipedia.org/wiki/Suction_cup) can stick to an appropriate surface in any direction as long as there is pressure on them from the outside.
Well a massive suction cup would have more force upon it.air moves at about 500 miles/hour.when u pour a drink,air is displacing it.suction is using air pressure.there is a force on everything.when you spin a 1kg metal disc for example at sat 2k revs a minute,you could throw it in the air and it might not come down providing it's still spinning at that speed.this would mean that no force is influencing it except the spinning.now,if I was correct,gravity would cease to exist as an attractive force?i could be wrong but it's a standard science experiment of making something lighter.no experiment has been done the way I say.if a force isn't moving,we can only measure what is moving so 7lbs could be more like a force equal to the density of the object.its clear water is lighter than air if not bonded.
 

Offline chiralSPO

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Re: How do gravity and buoyancy relate?
« Reply #30 on: 25/06/2015 21:11:19 »
spinning a disk does not make it lighter (actually, if you can spin it really, really fast, it would get slightly heavier--but that's beside the point).

spinning a disk can make it easier to lift, but that has to do with torque, not gravity. (
)
 

Offline PmbPhy

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Re: How do gravity and buoyancy relate?
« Reply #31 on: 26/06/2015 01:51:10 »
Quote from: chiralSPO
(actually, if you can spin it really, really fast, it would get slightly heavier--but that's beside the point).
By this he's referring to a relativistic effect that I derive here: http://home.comcast.net/~peter.m.brown/sr/rotating_cylinder.htm
 

Offline rmolnav

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Re: How do gravity and buoyancy relate?
« Reply #32 on: 26/06/2015 06:21:51 »
English is not my mother tongue, so I could be wrong in relation to most precise definition of PULL. But the way I put it in #20 regarding gravity attraction is very widely used in scientific literature:
https://www.google.es/?gfe_rd=cr&ei=pJmGVfP0JMyA8Qf0rICICg&gws_rd=ssl#q=sunīs+pull

PD: Sorry I said Archimedes in Spanish, with "qu" instead of "ch" ...

 
 

Offline PmbPhy

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Re: How do gravity and buoyancy relate?
« Reply #33 on: 26/06/2015 06:55:38 »
English is not my mother tongue, so I could be wrong in relation to most precise definition of PULL. But the way I put it in #20 regarding gravity attraction is very widely used in scientific literature:
https://www.google.es/?gfe_rd=cr&ei=pJmGVfP0JMyA8Qf0rICICg&gws_rd=ssl#q=sunīs+pull

PD: Sorry I said Archimedes in Spanish, with "qu" instead of "ch" ...
It's best to forget all this nonsense about "push" and "pull" because those terms are rarely, if ever, used in physics. In fact in all the physics texts that I've read in the last 35 years I've never once seen it used. The only related term with any meaning is force.
 

Offline gazza711

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Re: How do gravity and buoyancy relate?
« Reply #34 on: 26/06/2015 11:01:43 »
spinning a disk does not make it lighter (actually, if you can spin it really, really fast, it would get slightly heavier--but that's beside the point).

spinning a disk can make it easier to lift, but that has to do with torque, not gravity. (
)
Well the effect is wherever you influence the direction.the point is weightlessness in a sense.the weight changes.why?if air moves incredibly fast,preventing its molecules from applying a force on an object because the object is moving faster and thus breaking its grip on the object.i bet the brown experiment could cause anti gravity or indeed does!
Lexus reckons it's got ah overboard on concrete apparantly.lol.wont use push and pull words again,that's for sure!
 

Offline chiralSPO

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Re: How do gravity and buoyancy relate?
« Reply #35 on: 26/06/2015 14:51:54 »
Well the effect is wherever you influence the direction.the point is weightlessness in a sense.the weight changes.

No, this experiment has nothing to do with weightlessness. It is not so difficult to lift the 19 kg flywheel if you are holding on to the wheel itself. Putting the wheel at the end of a stick and trying to lift from the other end introduces a lot of torque, and that is why it is difficult to lift. Again, lifting from the end of the stick close to the flywheel is not so hard, but lifting from the far end is hard. This torque is eased when the flywheel is spinning, but the mass and weight remain (effectively) constant.
 

Offline gazza711

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Re: How do gravity and buoyancy relate?
« Reply #36 on: 26/06/2015 15:01:59 »
Well the effect is wherever you influence the direction.the point is weightlessness in a sense.the weight changes.

No, this experiment has nothing to do with weightlessness. It is not so difficult to lift the 19 kg flywheel if you are holding on to the wheel itself. Putting the wheel at the end of a stick and trying to lift from the other end introduces a lot of torque, and that is why it is difficult to lift. Again, lifting from the end of the stick close to the flywheel is not so hard, but lifting from the far end is hard. This torque is eased when the flywheel is spinning, but the mass and weight remain (effectively) constant.
It could have been 50kg.i think u missed the point.
 

Offline chiralSPO

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Re: How do gravity and buoyancy relate?
« Reply #37 on: 29/06/2015 13:33:56 »
No, you have missed the point. watch the video I posted again, it gives an excellent explanation of the phenomenon.
 

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Re: How do gravity and buoyancy relate?
« Reply #37 on: 29/06/2015 13:33:56 »

 

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