Buoyant Force and Submarines

[deleted647690]

I'm trying to imagine how submarines work in terms of buoyant force. As a sub takes on water, doesn't that mean that the amount of water the submarine is displacing would be less, so that the weight of the water that is actually displaced is less, so it would experience less of a buoyant force? When I think about it that way, it doesn't make sense.
I'm imagining it as a circle, and when the circle becomes half filled, it it is displacing less of the water around it.

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[wizzed101]

While completely submerged, the buoyant force on a submarine remains constant no matter what the submarine does.

 

[deleted647690]

While completely submerged, the buoyant force on a submarine remains constant no matter what the submarine does.

So then the only think changing is the weight of the submarine. But isn't it technically displacing less water if it takes on water?

 

[majikarp]

Don't think too much into this.

The water displaced is defined by the volume of the submarine. Taking in the water will increase the density within that volume of the submarine. However, since the buoyant force is defined by density (of displaced fluid) x volume x gravitational constant, the buoyant force is constant even if you take in water into the submarine. What changes when you take in water is the gravitational force created by the weight of the submarine, which increases due to increased density.