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Positive buoyancy occurs when an object is lighter than the fluid it displaces. The object will float because the buoyant force is greater than the object's weight.

But I also read,

buoyancy force for a partially submerged body (like a sailing boat) must be equal to the weight of the body

How can both statements be correct? Is the first one referring to the fact that the Body is wholly submerged, so the fluid's upthrust would be greater than the objects weight causing it to move upwards to the surface, where, the volume of water displaced decreases such that the buoyancy force decreases to become equal to the weight?

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  • $\begingroup$ Push the sailing boat down a bit, and it will pop back up, because (when pushed down) its buoyancy is greater than its weight. $\endgroup$ – hdhondt Oct 6 at 9:05
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The answer to both your questions in the last paragraph is yes. You understood it correctly.

The first sentence is not carefully worded, instead of "buoyant force is greater" is should say something like "buoyant force [on the fully submerged body] is greater".

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