Buoyant Force

[jjunior]

Hello, i just wanted to clear a small point,

Is it true to say that the buoyant force associated with 3 ball sinking, or stationary, or rising have the same buoyant force? knowing that they have the same volume and are being placed in the same medium.
But if the same ball is floating, maybe 30% above water, then the buoyant force is less than when it is rising is it correct? Since buoyant force depend on the volume being displaced?

thank you

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[navho77]

Correct. All buoyant force depends on is volume of fluid displaced. If something is floating, it means the buoyant force is exactly equal to the force of gravity down on the object. While it's rising, the object is experiencing a buoyant force greater than it's weight, mainly because it displaces the maximum amount of volume, thereby ensuring a maximal buoyant force, which we are assuming is greater than the weight, and so there is a net force. For the forces to balance (as in floating), a lesser volume of the fluid has to be displaced, and so the object rises and floats to where ever the weight of the volume of fluid displaced is exactly equal to the force of gravity. Since we already said the weight is less than the initial buoyant force when submerged (hence, the rising and floating), the buoyant force when floating must be less than the buoyant force when rising.

And yes, while submerged, the buoyant force is the same at any point beneath the surface of the fluid. Whether the object floats or sinks is entirely dependent on the NET force.

 

[jjunior]

thank you for your reply!