AVR-Chat

Brian wrote:
> I think I understand what you are saying. I know pressure is equal on all sides. So as the ball desends in the water the point of Bouyancy would raise from the center of the ball. Would this cause it to rise faster at deaper depths?

If it were a balloon it'd be the opposite.  The buoyancy of an object is 
the weight of the fluid that the object displaces.  If you had a balloon 
it would shrink in volume as it was pulled further under water, with its 
reduction is volume so too comes a reduction in its buoyancy (as per 
Archimedes).  This means that it would actually displace more (and 
become more buoyant) as it rose from the depths.  Water does not 
compress so it will be a constant weight at every depth.  Our ping pong 
ball won't compress much in only 15m of fluid so we can pretty much 
assume that its buoyancy will remain a constant at every depth. This 
leads us to an interesting depth gauge.  If you had a device that was 
designed to compress (and not be crushed at the maximum depth) you could 
put that at the bottom of the tank and measure the compression.  That 
compression would be directly correlated to the amount of fluid in the 
tank.  No bouncing of radio or sound waves, no moving parts (or not 
moving very much anyway).

DLC

> Brian
> 
> --- In AVR-Chat@yahoogroups.com, Phil Birkelbach <phil@...> wrote:
>> That is correct.  A cubic foot of water weighs considerably more than  
>> 10 oz.  You could take that thing to the bottom of the Gulf and let it  
>> go and it'll shoot straight back up.  This does assume that it doesn't  
>> get crushed somewhere along the way.  Pressure does not matter.  The  
>> assumption that pressure is only acting on the bottom is a bad one.   
>> The pressure pushes up, down sideways and every direction all at  
>> once.  The only pressure difference is the difference in the head  
>> pressure of the water from the top of the object to the bottom of the  
>> object and this is actually what causes it to be buoyant in the first  
>> place.  This pressure difference is constant at all depths (Assuming  
>> the density change of the water is negligible.  Which is a good  
>> assumption at 15m but probably not at the bottom of the Gulf).  The  
>> force pushing up on the object is the difference between the objects  
>> weight and the weight of the fluid it displaces.  This is true of any  
>> object in any fluid, including air.  Yes you are being lifted up by  
>> the atmosphere, but you're just too darn heavy to notice.
>>
>> Phil
>>
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-- 
Question with boldness even the existence of a God;
because, if there be one, he must more approve of the
homage of reason, than that of blind-folded fear.
Thomas Jefferson
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