Chapter-9 The Behavior of Fluids

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Chapter-9 The Behavior of Fluids
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Outline

• 1 Pressure, Hydraulics, and Pascals Principle
• 2 Atmospheric Pressure and the Behavior of Gases
• 3 Archimedes Principle
• 4 Fluids in Motion
• 5 Bernoullis Principle
• Everyday Phenomenon
• Throwing a Curve Ball

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A steel boat floats, but a piece of metal sinks.
Why?
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Fluids
Fluids are materials that can flow, gases and
liquids. Air is the most common gas, and moves
from place to place as wind. Water is the most
familiar liquid.
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Pressure
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Tire Pressure
People who have fixed a flat tire know something
about pressure.
In colliding with the inner walls of the tire,
the air molecules (blue dots) exert a force on
every part of the wall surface.
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Pressure
The pressure P exerted by a fluid is defined as
the magnitude F of the force acting perpendicular
to a surface divided by the area A over which the
force acts
The SI unit for pressure newton/meter2 (N/m2)
pascal (Pa).
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Area of a square
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Area of a rectangle
Width
Length
Area Length x Width.
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Area of a circle
d
Area ?r2, d diameter 2r.
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Pressure acts everywhere
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Pressure Acts Everywhere
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Pascal's Principle
Any change in the pressure applied to a
completely enclosed fluid is transmitted
undiminished to all parts of the fluid and the
enclosing walls.
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Hydraulic Jack
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Car Lift
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Hydraulic Car Lift
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E5
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Atmospheric Pressure
Atmospheric pressure at sea level is 1.013 105
Pa, which is sufficient to crumple a can if the
inside air is pumped out.
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Mercury Barometer
At sea level, Height of mercury h 76 cm.
Atmospheric pressure 76 cm of Hg. (76 cm 760
mm 29.9 inch)
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Variations in atmospheric pressure
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Density of air decreases as the altitude increases
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9.3Archimedes Principle Archimedes of Syracuse
(287BC-212BC)
Much of Archimedes fame comes from his
relationship with Hiero, the king of Syracuse,
and Gelon, Hiero's son. At one time, the king
ordered a gold crown and gave the goldsmith the
exact amount of gold to make it. When Hiero
received it, the crown had the correct weight but
the monarch suspected that some silver had been
used instead of the gold. Since he could not
prove it, he brought the problem to Archimedes.
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Eureka
One day while considering the question, "the wise
one" entered his bathtub and recognized that the
amount of water that overflowed the tub was
proportional the amount of his body that was
submerged. This observation is now known as
Archimedes' Principle and gave him the means to
solve the problem. He was so excited that he ran
naked through the streets of Syracuse shouting
"Eureka! eureka!" (I have found it!). The
fraudulent goldsmith was brought to justice.
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Buoyant Force
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Viscosity
A measure of the frictional forces between the
layers of a fluid producing resistance to flow.
Highly viscous fluids flow slowly.
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The velocity increases rapidly from the wall
inward for a low-viscosity fluid but more
gradually for a high-viscosity fluid
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Laminar and Turbulent flow
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9.5 Bernoullis Principle
For steady flow, the speed, pressure, and
elevation of an incompressible and nonviscous
fluid are related by an equation discovered by
Daniel Bernoulli (17001782). The sum of the
pressure plus the kinetic energy per unit volume
of a flowing fluid must remain constant.
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The pressure of a moving fluid is greater when
the fluid velocity is smaller.
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Demonstrating Bernoullis Principle
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Lift on an airplane wing
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Airplane
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A batter is fooled by a curveball
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Spinning Baseball
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Curveball Pitch