advanced physics chapter 10 fluids. chapter 10 fluids 10.1 density and specific gravity 10.2...
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Advanced Physics
Chapter 10Fluids
Chapter 10 Fluids 10.1 Density and Specific Gravity 10.2 Pressure in Fluids 10.3 Atmospheric and Gauge Pressure 10.4 Pascal's Principle 10.5 Measurement of Pressure 10.6 Buoyancy and Archimedes’ Principle 10.7 Fluids in Motion 10.8 Bernoulli’s Principle 10.9 Applications of Bernoulli’s Principle 10.10 Viscosity 10.11 Flow in Tubes 10.12 Surface Tension and Capillarity 10.13 Pumps; the Heart and Blood Pressure
10.1 Density and Specific Gravity
Four phases of matter (each with different properties)
Solid Liquid Gas Plasma Fluids are anything
that can flow so they are ?
10.1 Density and Specific Gravity
Density- how compact an object is
Ratio of mass to volume
= m/V• Many units for densitySpecific Gravity- ratio
of the density of a substance to the density of a standard substance (usually water)
• No units (Why?)
10.2 Pressure in Fluids
Pressure—a force applied per unit area
P = F/A Units Pascal
(N/m2)
10.2 Pressure in Fluids
Important properties of fluids at rest: Fluids exert a pressure in all
directions The force always acts perpendicular
to the surface it is in contact with The pressure at equal depths within
the fluid is the same
10.2 Pressure in Fluids
Pressure variation with depth
P = F/A = gh
Change in pressure with change in depth
P = gh
10.3 Atmospheric and Gauge Pressure
Atmospheric Pressure (PA)—the pressure of the Earth's atmosphere at sea level
1atm = 101.3kPa = 14.7 lbs/in2 = 760 mmHg
10.3 Atmospheric and Gauge Pressure
Gauge Pressure (PG)—the pressure measured on a pressure gauge
Measures the pressure over and above atmospheric pressure
P = PA + PG
P = Absolute pressure
10.4 Pascal's Principle
Pascal's Principle states that pressure applied to a confined fluid increases the pressure throughout by the same amount
Example: hydraulic lift
10.4 Pascal's Principle
Pascal's PrincipleExample: hydraulic lift
Pin = Pout Fout/Aout =
Fin/Ain
Fout/Fin = Aout/Ain
Fin
Fout
10.5 Measurement of Pressure
Manometer—tubular device used for measuring pressure
To measure pressure with a manometer remember the Jenke quote “Nothing sucks in Science it just blows”
10.5 Measurement of Pressure
Manometer—tubular device used for measuring pressure
Types: Open-tube
manometer Closed-tube
manometer (barometer)
10.5 Measurement of Pressure
Open-tube manometer
both ends of tube are open; one is connected to the container of gas and the other is open to the atmosphere
GAS
10.5 Measurement of Pressure
Open-tube manometer
P = Po + ghWhere: P = pressure of gas Po = atmospheric
pressure gh = pressure of
fluid displaced
GAS
10.5 Measurement of Pressure
Closed-tube manometer
one end of tube is open; one is connected to the container of gas is open and the other is sealed
GAS
10.5 Measurement of Pressure
Closed-tube manometer
P = Po + gh But since it is
closed Po = 0 so…..
P = gh
GAS
10.5 Measurement of Pressure
Barometer-closed-tube manometer inverted in a cup of mercury used to measure atmospheric pressure
P = gh Where is the density
of mercury (13.6 x 103 kg/m2)
10.6 Buoyancy and Archimedes’ Principle
Objects submerged in a fluid appear to weigh less than they do outside the fluid
Many objects will float in a fluid
These are two examples of buoyancy
10.6 Buoyancy and Archimedes’ Principle
Buoyant force—the upward force exerted on an object in a fluid.
It occurs because the pressure in a fluid increases with depth
10.6 Buoyancy and Archimedes’ Principle
Buoyant force (FB) The net force due to
the force of the fluid down (F1) and up (F2)
FB = F2 – F1
Since F = PA =FghA FB = FgA(h2—h1) FB = FgAh = FgV
F1
F2
h1h2
h=h2-h1
10.6 Buoyancy and Archimedes’ Principle
Archimedes’ Principle The buoyant force on a
body immersed in a fluid is equal to the weight of the fluid displaced by that object
FB = FgV = mFg To be in equilibrium the
weight of object must be the same as the weight of fluid displaced so that it is equal and opposite FB
FB
Wt = mg
10.6 Buoyancy and Archimedes’ Principle
Archimedes’ Principle So when an object is
weighed in water its apparent weight (in fluid, w’) is equal to its actual weight (w) minus its buoyant force (FB)
w’ = w – FB
w/(w—w’) = o/ F
FB
Wt = mg
10.6 Buoyancy and Archimedes’ Principle
Archimedes’ Principle Also relates to objects
floating in fluid Object floats in a fluid if
its density is less than the density of the fluid
The amount submerged can be calculated by
Vdispl/Vo = o/ F
FB = FVdisplg
W= mg=oVog
10.7 Fluids in MotionFluid Dynamics
(Hydrodynamics) The study of fluids in
motionTwo types of fluid flow: Streamline (laminar)
flow--particles follow a smooth path
Turbulent flow—small eddies (whirlpool-like circles) form
10.7 Fluids in Motion Turbulent flow
causes an effect called viscosity due to the internal friction of the fluid particles
10.7 Fluids in Motion Lets study the
laminar flow of a liquid through an enclosed tube or pipe
Mass Flow rate is the mass of fluid (m) that passes a given point per unit time (t)
l1l2
A1
A2
v1
v2
10.7 Fluids in MotionMass Flow rate The volume of fluid
passing through area A1 in time t is just A1 l1 where l1 is the distance the fluid moves in time t.
Since the velocity of fluid passing A1 is v = l1/ t, the mass flow rate m1/ t through area A1 is
m1/ t = 1A1v1
l1l2
A1
A2
v1
v2
10.7 Fluids in Motion
Mass Flow rate m1/ t = 1A1v1
Since what flow through A1 must also flow through A2 then
m1/ t = m2/ t So 1A1v1 = 2A2v2
l1l2
A1
A2
v1
v2
10.7 Fluids in MotionMass Flow rate 1A1v1 = 2A2v2
Since for most fluids density doesn’t change (too much) with an increase in depth so it can be cancelled out.
Equation of continuity A1v1 = A2v2
[Av] represents the volume rate of flow V/t of the fluid
l1l2
A1
A2
v1
v2
10.7 Fluids in Motion Since the volume
rate of flow V/t of the fluid is the same in all parts of the pipe the velocity through smaller diameter sections must be greater than through larger diameter sections
l1l2
A1
A2
v1
v2
10.8 Bernoulli’s PrincipleBernoulli’s Principle—
where the velocity of a fluid is high, the pressure is low and where the velocity is low the pressure is high.
This makes sense; if the pressure was larger at A2 then it would back up fluid in A1 so its slow down from A1to A2 but it actually speeds up.
l1l2
A1
A2
v1
v2
P1
P2
10.8 Bernoulli’s Principle
Bernoulli’s Equation (derivation in Book)
P1 + 1/2v12 + gy1 =
P2 + 1/2v22 + gy2
Or P + 1/2v2 + gy =
constant This is based on the
work needed to move the fluid from Part 1 to Part 2 of the tube.
y1
y2
l1
l2
A1
A2
V1
P1
V2
P2
10.9 Applications of Bernoulli’s Principle
Special cases of Bernoulli’s Equation:
Liquid flowing out of an open container with a spigot at the bottom
Since both P’s are atmospheric pressure and v2 is almost zero
1/2v12 + gy1 = gy2
v1 = (2g(y2 – y1))1/2
V2 = 0
v1
Y2 – y1
10.9 Applications of Bernoulli’s Principle
Special cases of Bernoulli’s Equation:
Liquid flowing but there is no appreciable change in height
P1 + 1/2v12 = P2 +
1/2v22
Example: your Physics toy
Read and Write Worksheet Read Sections
10.10 –10.13 Answer the
questions written on ½ sheet of paper