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Buoyancy or Net Upward Force?


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Hey all,

So I'm doing an assignment on swimsuits and their effect on performance, and I decided to make one of the factors I consider buoyancy. This was because numerous sites talked about how buoyancy is vital, and how FINA has even imposed regulations on it to keep the playing field fair. They say that this is achieved by using lighter foam-like materials, for example polyurethane, to increase buoyancy, but there's one problem. After some extra research, I can find no articles that say that buoyancy is depended on the object's weight or density at all. Buoyancy appears to be a single force that pushes upwards, and is dependent on the object's volume, the liquid's density and the force of gravity, and not the object's weight. What I think has happened is that the articles have misused the word buoyancy, instead of net upward force (or its equivalent), as the object's weight only seems to comes into play when you balance its weight in newtons against the buoyant force and come up with its net upward force. So in essence, my question is this. Are all of the websites wrong, or do I just have a incomplete definition of buoyancy? If so, could you point me to a reliable source which holds the correct one? And I also wanted to make sure that there isn't another word for an object's net upward force in water, as that would be cumbersome to say all of the time in my report.

Thanks in advance, Dan

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Buoyancy would be correct to use for both. Air and water are both formally considered fluids.

Buoyancy is ultimately due to Earth's gravity pulling on whatever fluid you are displacing.

Fluids: Archimedes' Principle | Paige's Physics Blog
A simpler way to say it is:
 
FB = mfl * g
or
Buoyant Force = Weight of the displaced Fluid
 

A wet-suit could help you to displace more fluid and increase your buoyancy that way.

 

Net force would be the Buoyant force minus the object's own weight.

 

Hopefully this helps, interesting question.

 

 

Edited by Endy0816
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2 hours ago, Uber-Dan said:

After some extra research, I can find no articles that say that buoyancy is depended on the object's weight or density at all. Buoyancy appears to be a single force that pushes upwards, and is dependent on the object's volume, the liquid's density and the force of gravity, and not the object's weight.

This is correct.  I have a balloon and a rock of the same volume, but very much different weight, but the buoyancy of both is the same: The weight of both is reduced by the same amount when submerged in say water.  The buoyant force on the rock is not enough to counter its weight, so it still sinks.  The force on the balloon is far greater than the force of its weight, so the balloon will rise to the surface.

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