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HW 10 Tips;
PHY 131 Sect. 10, 11, 15; Fall 2010
Prof. Pascuzzi
HW 10 covers the basics of Static & Dynamic Fluids from Chapter 13
Information you may need;
HYDROSTATICS
(i.e. stationary liquids);
Pressure, Gauge Pressure & Density;
(note that from the density equation, you can also get the mass of an object by;
)
Buoyant Force;
Pascal’s Principle (Pressure within a fluid in a closed container is transmitted undiminished throughout
the liquid)
HYDRODYNAMICS
(i.e. liquids in motion);
Equation of Continuity (
Mass flow rate; unit = kg/sec
)
;
Equation of Continuity (
Volume flow rate; unit = m
3
/sec
);
Bernoulli’s Equation
;
Poiseuille’s equation;
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Problem 1 “Archimedes’ Principle”
This problem is a great qualitative description of buoyant force and Archimedes’ principle.
Hints on using the equation for buoyant force;
Remember that the liquid will provide an upward
support force for a floating object, which is equivalent to the weight of the liquid that the floating object pushes
aside (i.e. displaces). As the object becomes more and more submerged, the amount of displaced liquid must
increase, and thus, so does the buoyant force provided by the liquid.
When the object is completely submerged,
the
maximum
buoyant force is exerted on the object (this is
) where the weight
mg
(or
)
of the displaced liquid is equal to the object’s weight (hence the subscripts above).
If the object sinks, the
buoyant force is exceeded by the object’s weight…thus, you can not only tell that an object floats if its density
is less than that of the liquid, but also if its weight exceeds the maximum buoyant force on it.
What happens if the object is floated in liquids of
different
density?
Think about it!
The denser the
liquid, the more weight it can support, so will the object float higher, or submerge further?
Similarly, what if a
less dense liquid is used?
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 Fall '03
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