Exploring the Impact of Air Pressure on Archimedes Law

• HWGXX7
In summary, Archimedes law does not account for the buoyancy of an object immersed in air. This is because the air pressure is the same on both the object and the water, and the effect is too small to be considered.
HWGXX7
Why isn't the influence of air pressure assimilated in Archimedes law?

If an obect is more dense than the fluid, it wil sink. That is clear, but suppose I could lower down de air pressue, so less force that tends to push the object tot the surface. Is there any situation possible of adjusting the air pressure to get an object just floating? Or is the influence of the air pressure in incompressible fluids not great, so change in pressure wouldn't be noticed very much?

But , think of it as an theoretical question.

The key factors are the density of the fluid and the object, with gravity the controlling force. Air pressure plays no role.

Air pressure plays no role.

The reason is that it can be neglected, is that correct?

HWGXX7 said:
The reason is that it can be neglected, is that correct?

Your question is confusing. The air pressure is the same on both the object and the water.

An object immersed in air experiences bouyancy.

I think it IS accounted for in Archimedes' law.

Or is the influence of the air pressure in incompressible fluids not great, so change in pressure wouldn't be noticed very much?
Have more faith in yourself !

In slide rule days the effect was too small to warrant consideration, but with today's umpteen-digit calculators I'm sure it could be included. Try it and see how many digits out it shows up.

From wiki,
http://en.wikipedia.org/wiki/Properties_of_water
Compressibility

The compressibility of water is a function of pressure and temperature. At 0 °C, at the limit of zero pressure, the compressibility is 5.1×10−10 Pa−1.[28] At the zero-pressure limit, the compressibility reaches a minimum of 4.4×10−10 Pa−1 around 45 °C before increasing again with increasing temperature. As the pressure is increased, the compressibility decreases, being 3.9×10−10 Pa−1 at 0 °C and 100 MPa.

The bulk modulus of water is 2.2 GPa.[29] The low compressibility of non-gases, and of water in particular, leads to their often being assumed as incompressible. The low compressibility of water means that even in the deep oceans at 4 km depth, where pressures are 40 MPa, there is only a 1.8% decrease in volume.[29]

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I think it IS accounted for in Archimedes' law.

I re-analysed it and atmospherical pressure cannot influence the dyncamic behaviour of a particle that is submerged complete. So there Archimedes law cannot account for it at all.

Air pressure plays a role in the buoyancy of Cartesian divers.

Correct, in general air pressure will influence the behaviour of any particle in contact with the air pressure. Once complete submerged this isn't the case anymore.
http://en.wikipedia.org/wiki/Buoyancy

grtz

HWGXX7 said:
Correct, in general air pressure will influence the behaviour of any particle in contact with the air pressure. Once complete submerged this isn't the case anymore.
http://en.wikipedia.org/wiki/Buoyancy
grtz
It does not have to be "in contact". The atmospheric pressure is transmitted through water. The pressure acting on the submerged body is the sum of atmospheric pressure and hydrostatic pressure. If the submerged body is flexible, the increase in atmospheric pressure may produce a change of its volume.

The results that atmospheric pressure does not directly influence buoyancy is due to the buoyancy depending on the pressure difference (or gradient) along the vertical direction.
Atmospheric pressure just adds a constant factor to the hydrostatic pressure and this has no contribution to the gradient.

It does not have to be "in contact".

Correct, made a mistake there. Difference in air pressure wil result in greater hydrostatic pressure, and therefore a greater upward force.
The object remains in static equilibrium because of difference in de weight of the air pushing downwards.

thank for all the help

1. How does air pressure affect Archimedes' Law?

Air pressure affects Archimedes' Law by changing the density of the surrounding air. This change in density can impact the buoyant force acting on an object, altering its ability to float or sink.

2. Can air pressure completely negate the effects of Archimedes' Law?

No, air pressure cannot completely negate the effects of Archimedes' Law. While air pressure can alter the buoyant force on an object, the law is still applicable and will still result in an upward force on the object.

3. How does the altitude affect air pressure and, in turn, Archimedes' Law?

As altitude increases, the air pressure decreases. This can affect the density of the surrounding air, which in turn can alter the buoyant force acting on an object. Therefore, the altitude can impact the accuracy of Archimedes' Law.

4. Can the temperature also impact air pressure and Archimedes' Law?

Yes, temperature can also impact air pressure and Archimedes' Law. As temperature increases, air molecules move faster and spread out, resulting in a decrease in air pressure. This change in air pressure can then affect the buoyant force acting on an object.

5. Are there any other factors besides air pressure that can influence Archimedes' Law?

Yes, there are other factors that can influence Archimedes' Law, such as the density of the object and the density of the fluid it is placed in. These factors can also impact the buoyant force and the ability of an object to float or sink.

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