Re: Boyancy and Gravity!

From: chris h fleming (chris_h_fleming_at_yahoo.com)
Date: 11/16/04 

Date: Tue, 16 Nov 2004 08:56:22 +0000 (UTC)

Gremlin <virtualadepts.nospam@gmail.com> wrote in message news:<Xns95A16F8E95E93Test@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 there were no atmosphere? By Gauss's law the atmosphere contributes
no gravitational force to us on the earth, but only to those in the
atmosphere or in outerspace. The difference felt by a space traveler
would depend on how much mass is in the atmosphere.

> If you look at a helium balloon it obviously has
> mass, yes.. but it has no actual weight..

I believe the balloon certainly does have weight. Try weighing it in a
vacuum. The balloon is just less dense than air, so it floats in air.
On the moon it would drop.

> if you were to measure it on a
> scale. So obviously air pressure factors in to somethings weight.

Gravity gives us weight that pushes us down. Air gives us buoyancy
that pushes us up. You seem to be saying that weight = gravity +
buoyancy. That is what is measured on a scale, but to a scientist
weight = gravity only.

> 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.

The scale would measure less the force of buoyancy. Which is just the
weight of a person sized amount of air.
So take a person as about 1/2 meter x 1/2 meter x 2 meters = 1/2
meter^3 volume.
And the density of air being 1.29 kilograms/meter^3.
A person sized amount of air would have a mass of about .6 kilograms
and what ever that would translate to in pounds on earth's surface

so that's the difference.

> Apparently the force of gravity keeps air around the earth.

Apparently

> 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!?

I think there is one simple thought experiment that proves this theory
wrong.

What happens when you open the door of a space shuttle (while in outer
space)? By your theory the air would stay in the ship because of
vacuum buoyancy. But the air will diffuse into outerspace! And you
probably know this.

If you are interested in these ideas, then you should study Newtonian
gravity, buoyancy, pressure, and diffusion.

Relevant Pages

  • Re: The weather and the many different factors that drive it...
    ... > winds travel upwards and suck air away from the surface of the Earth ... > like a giant vacuum cleaner, decreasing the air pressure above the ... > the levels in the atmosphere involved. ... > Troposphere where in reality the Stratosphere has a part to play. ...
    (sci.geo.meteorology)
  • Re: Boyancy and Gravity?
    ... > What would gravity on the earth be like without this air pressure, ... So obviously air pressure factors in to somethings weight. ... > Apparently the force of gravity keeps air around the earth. ...
    (sci.physics)
  • Re: cheap lunar gear & base (spin-off of superhero flight)
    ... The Apollo 1 fire happened not just because of a pure oxygen atmosphere, ... test the spacecraft's ability to hold pressure in a vacuum, ... switching air pressures instantaneously. ... If the teleporter is able to take the super as a passenger and is always ...
    (rec.arts.sf.science)
  • Re: electrolysis
    ... molecules from the atmosphere? ... Oxygen is commercially distilled from air-see liquefaction of air. ... Also check the composition of Earth's atmosphere? ... pressure ...
    (sci.chem)
  • Re: cheap lunar gear & base (spin-off of superhero flight)
    ... but because they used a _16 psi_ pure oxygen atmosphere. ... test the spacecraft's ability to hold pressure in a vacuum, ... There'll be unpleasant ear-popping, perhaps, if your teleporter is ... switching air pressures instantaneously. ...
    (rec.arts.sf.science)