buoyant force in liquid vs. air

Discussion in 'MCAT Study Question Q&A' started by SaintJude, 03.01.12.

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1. SaintJude

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A cube of wood whose side are each 10 cm weight 16 N in air. When half submerged in an unknown liquid, it weights only 10 N.

Why is the buoyant force the difference between an object's weight in air and that in liquid? (So in this question, Fb=6?)

Last edited: 03.01.12
3. chiddler 5+ Year Member

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Because the force depends on the density of the fluid that contains it.

4. SaintJude

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Don't understand what you just said.

5. milski1K member 5+ Year Member

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By weight in the water they mean the force pulling down the cube. That's its weight minus the buoyant force. In air the weight is just that - the weight.

6. SaintJude

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1.) How did you know the "weight in the water" is actually the "force pulling down the cube. " ?

Last edited: 03.01.12
7. chiddler 5+ Year Member

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sorry i misunderstood the question.

8. milski1K member 5+ Year Member

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What else could it be? Weight is the force that Earth exerts on the object by gravity. So if you want to be very precise, the weight should be the same in both cases. But it's customary to refer as weight to the force that pulls a body down towards the Earth.