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Old Aug 12th 2014, 07:30 PM   #1
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Weight of object = Force of buoyancy: can I use this when density of object is greatr

My text book says that for floating objects we can use the equation weight of the object equals to force of buoyancy. They call this equation, floating object in equilibrium on surface. However, what happens when the density of the object is greater than the density of the fluid and the object sinks? Can we still use the floating object equation?
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Old Aug 13th 2014, 04:39 AM   #2
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The equation you're referring to is for the case that the object is in equilibrium with the fluid, and neither sinks nor rises. Think of a submarine submerged and hanging motionless under water - in this condition the overall density of the sub equals the density of the water it is submerged in. If the sub captain decides to descend deeper, he lets water into the ballast tanks so that the sub becomes heavier and hence more dense than the water, and the sub sinks. Under this condition the weight of the sub is greater than he weight of water it displaces, so no - the equation is changed to weight of object > force of buoyancy.
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Old Aug 13th 2014, 06:44 AM   #3
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Ahhhh thank you ChipB! I was unfocused yesterday studying all day!
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