Advanced Physics Chapter 10 Fluids. Chapter 10 Fluids 10.1 Density and Specific Gravity 10.2 Pressure in Fluids 10.3 Atmospheric and Gauge Pressure 10.4

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)


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


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”


Manometer—tubular device used for measuring pressure

Types: Open-tube

manometer Closed-tube

manometer (barometer)


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


Open-tube manometer

P = Po + ghWhere: P = pressure of gas Po = atmospheric

pressure gh = pressure of

fluid displaced

GAS


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


Closed-tube manometer

P = Po + gh But since it is

closed Po = 0 so…..

P = gh

GAS


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


Buoyant force—the upward force exerted on an object in a fluid.

It occurs because the pressure in a fluid increases with depth


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


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


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


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

Documents

Advanced Physics Chapter 10 Fluids. Chapter 10 Fluids 10.1 Density and Specific Gravity 10.2 Pressure in Fluids 10.3 Atmospheric and Gauge Pressure 10.4