Re: Boyancy and Gravity?

From: EL (hemetis_at_hotmail.com)
Date: 11/15/04 

Date: 14 Nov 2004 16:06:51 -0800

Gremlin <virtualadepts.nospam@gmail.com> wrote in message
news:<Xns95A16F3179664Test@216.168.3.44>...
> The average atmospheric pressure at Earth's surface is about 14.6 pounds
> per square inch, which is about 100,000 pascals.
>
> What would gravity on the earth be like without this air pressure, with 0
> pascals of air pressure? If you look at a helium balloon it obviously has
> mass, yes.. but it has no actual weight.. if you were to measure it on a
> scale. So obviously air pressure factors in to somethings weight. My
> question is how much would an average person weigh if it were not for air
> pressure? Or in general any discussion about the topic.
>
> Apparently the force of gravity keeps air around the earth. Perhaps though
> the air is just more dense than the near vacuum of space so it collects
> itself into on place. That is my theory, as what gravity actually is..
> Just an effect of buoyancy. No need to argue with me about it because I
> don't have any evidence to support my idea.. yet. Solids also collect
> themselves because of buoyancy in near vacuum and in air.. As does water
> etc. This is why a rock will sink in water, and water will sink in air..
> and helium will rise in air. Everything though will sink in the near
> vacuum of space though because buoyancy is caused by density and vacuum is
> the least dense of everything. It is just there is no 'down' for anything
> to sink in, in vacuum so everything just collects together and creates a
> down consistent with that collection of matter.
>
> What do you think!?

[EL]
I think you are a genius.
I am also very sincere about it because of the rationality of your
reasoning.
Now let us discuss your idea a bit deeper.
Firstly, there is great common sense in what you say, but how can we
formalise that common sense into useful scientific information!
Secondly, you noticed a problem in finding a favourite direction that
can be called the center of gravity in absolute vacuum.

Buoyancy is by definition a phenomenon related to fluids, pressure and
density as well as displacement under the equilibrium of forces.

We can rest a cube of iridium on top of a cube of aluminium without
observing any density related displacement in room temperature.
If we take this set and raise the temperature to above the melting
point of aluminium the iridium cube shall sink in the molten
aluminium. We can do that experiment by using a cube of iron placed on
ice before melting ice.

If we take any regular-shaped dense solid to the outer space and
release a volume of a fluid adjacent to that solid, we expect the
fluid to distribute itself such that it encapsulates the solid surface
obeying the laws of fluid cohesion, fluid-solid adhesion, gravitation
and buoyancy.

However, we have a very interesting riddle here.

Assume that we made a cup out of solid Iridium or Osmium (highest
density metals), taking the shape of exactly half of a spherical
shell.
If we added liquid helium (the volume of which is exactly equal to the
volume of the cup's inner cavity), as a fluid, on the convex side of
that cup, what shall happen to that liquid material?

Do you think it should:
 
1- move to the concave side completely and fill the cup?
2- be distributed evenly so that it becomes a liquid "atmosphere" with
a constant fluid depth normal to the solid surface on both sides?
3- form a spherical shell that encapsulates the metallic cup?
4- form a "solid-shaped" liquid-sphere into which the cup "sinks"
deforming it?
5 - redistribute itself on both sides of the cup along the axis of
symmetry to form a liquid sphere intersecting the solid cup?
6- most of the liquid volume moves to the virtual center of mass of
the solid cup keeping some of the liquid to balance out the newly
formed center of mass of the mixture?
7- non of the above, offering a different proposal?

Have fun. :-)

EL

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