A question on buoyancy confusing too many Chinese?

[doG]

Artw, consider the buoyancy of crocodilians. Their body mass(the stone) remains the same and the quantity of air in their lungs(the balloon) remains the same. They go up and down by controlling the volume of their lungs. When they want to rise they push their liver back which allows the lungs to expand thereby changing the volume of their lungs. This doesn't change the quantity of air in their lungs, just its displacement. When they want to sink they allow their liver to move up against the lungs to compress them. By fine tuning the volume of their lungs they can precisely control their buoyancy.

[J.C.MacSwell]

Edit: I made no post

Edited July 30, 2011 by J.C.MacSwell

[ArtW]

I am wrong.

I found the mistake.

Wikipedia gives me the best answer.

Thank you all.

 

From Wikipedia:

Compressible objects

As a floating object rises or falls, the forces external to it change and, as all objects are compressible to some extent or another, so does the object's volume. Buoyancy depends on volume and so an object's buoyancy reduces if it is compressed and increases if it expands.

If an object at equilibrium has a compressibility less than that of the surrounding fluid, the object's equilibrium is stable and it remains at rest. If, however, its compressibility is greater, its equilibrium is then unstable, and it rises and expands on the slightest upward perturbation, or falls and compresses on the slightest downward perturbation.

Submarines rise and dive by filling large tanks with seawater. To dive, the tanks are opened to allow air to exhaust out the top of the tanks, while the water flows in from the bottom. Once the weight has been balanced so the overall density of the submarine is equal to the water around it, it has neutral buoyancy and will remain at that depth.

The height of a balloon tends to be stable. As a balloon rises it tends to increase in volume with reducing atmospheric pressure, but the balloon's cargo does not expand. The average density of the balloon decreases less, therefore, than that of the surrounding air. The balloon's buoyancy decreases because the weight of the displaced air is reduced. A rising balloon tends to stop rising. Similarly, a sinking balloon tends to stop sinking.

 

 

 

[csmyth3025]

I am wrong.

I found the mistake.

Wikipedia gives me the best answer.

Thank you all.

 

From Wikipedia:

Compressible objects

As a floating object rises or falls, the forces external to it change and, as all objects are compressible to some extent or another, so does the object's volume. Buoyancy depends on volume and so an object's buoyancy reduces if it is compressed and increases if it expands.

If an object at equilibrium has a compressibility less than that of the surrounding fluid, the object's equilibrium is stable and it remains at rest. If, however, its compressibility is greater, its equilibrium is then unstable, and it rises and expands on the slightest upward perturbation, or falls and compresses on the slightest downward perturbation.

On the subject of compressibility as it relates to buoyancy, it's interesting to note the following:

 

...The Trieste consisted of a float chamber filled with gasoline for buoyancy, with a separate pressure sphere...

 

-and-

 

...Gasoline (petrol) was chosen as the float fluid because it is less dense than water, yet relatively incompressible even at extreme pressure, thus retaining its buoyant properties and negating the need for thick, heavy walls for the float chamber...

(ref. http://en.wikipedia....e_(bathyscaphe) )

 

Chris

[ArtW]

On the subject of compressibility as it relates to buoyancy, it's interesting to note the following:

 

 

(ref. http://en.wikipedia....e_(bathyscaphe) )

 

Chris

 

 

YES!!

I KNOW IT NOW.

[ArtW]

hi,i am back

[Dinosaur19006]

As you push the balloon down the volume decreases & the density increases.

 

If the water is deep enough, the density will become more than the density of water & the balloon will sink to the bottom.

 

I do not know if earthly oceans are deep enough for this to occur. My WAG is that Earthly oceans are not deep enough

 

SWAG (Sophisticated Wild Ass Guess) is more accurate than a WAG.