*Archimedes’
Principle: body immersed in a fluid experiences a buoyant force equal to weight
of fluid it displaces.*

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B

*Which body is heavier? A or
B*

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*Which fluid is denser? A or
B*

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__Buoyant
force F _{B}__

_{ }

**F _{B}
= weight of displaced fluid**

** **

** = ****g**** x (submerged volume of
body)**

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__HYDROMETER____: __

Instrument
used to measure S.G of a fluid is based on principle of buoyancy

- Which fluid is more
dense?

**What
is stability? **

**A
body subjected to small angular displacement will try to get back to original.**

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**Or,
moments that try to rotate body get it back to where it was before.**

· **Two moments try to restore
body.**

· **F _{B}xa and Wxa**

· **Lesser of the two is called
“Righting Moment”**

**Righting moment = Wxa , if W<F _{B}**

** =
F _{B }xa, if W>F_{B}**

**CRITERION
FOR STABILITY OF A FULLY SUBMERGED BODY IS THAT CENTER OF BUOYANCY MUST BE
ABOVE CENTER OF GRAVITY.**

· Body will rise until W=F_{B
}

· At equilibrium, W and F_{B}
are equal and opposite and lie in the same vertical line

· **Recall, for a fully
submerged body center of buoyancy (B)and center of gravity (G)are fixed and the
criterion for stability is that B is above G
**

· **For a floating body, B can
move relative to G, depending on how much fluid is displaced.
**

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· **Stability of floating body
depends on its shape.**