Physics of Technology
PHYS 1800
Lecture 20
Introduction
Fluids and Pressure
Section 0
Lecture 1
Slide 1
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Fluids and Pressure
Lecture 20 Slide 1
PHYSICS OF TOF
ECHNOLOGY
- PHYS 1800
PHYSICS
TECHNOLOGY
ASSIGNMENT SHEET
Spring 2009Spring
Assignment
Sheet
2009
Date
Day
Lecture
Chapter
Feb 16
M
Presidents Day
17
Tu
Angular Momentum (Virtual Monday)
18
W
Review
19
H
Test 2
20
F*
Static Fluids, Pressure
Feb 23
M
Flotation
25
W
Fluids in Motion
27
F*
Temperature and Heat
Mar 2
M
First Law of Thermodynamics
4
W
Heat flow and Greenhouse Effect
6
F*
Climate Change
Mar 9-13
M-F
Spring Break
Mar 16
M
Heat Engines
18
W
Power and Refrigeration
20
F*
Electric Charge
Mar 23
M
Electric Fields and Electric Potential
25
W
Review
26
H
Test 3
27
F*
Electric Circuits
Mar 30
M
Magnetic Force Review
Apr 1
W
Electromagnets
3
F
Motors and Generators
Apr 6
M
Making Waves
8
W
Sound Waves
10
F*
E-M Waves, Light and Color
Apr 13
M
Mirrors and Reflections
Introduction
Section
0 Lecture 1 Slide 2
15
W
Refraction and Lenses
17
F*
Telescopes and Microscopes
Apr 20
M
Review
22
W
Seeing Atoms
24
F
The really BIG & the really small
INTRODUCTION TO Modern Physics PHYX 2710
May
1
F
Final Exam: 09:30-11:20am
No Class
8
5-8
5-8
9
9
9
10
10
10
No Classes
11
11
12
12
13
9-12
13
14
9-12
14
15
15
16
17
17
17
1-17
18 (not on test)
21 (not on test)
Homework Due
-
6
7
8
-
9
10
11
No test week
12
Fall 2004
* = Homework Handout
*Homework Handout
Physics of Technology—PHYS 1800
Spring 2009
Fluids and Pressure
Lecture 20 Slide 2
Physics of Technology
PHYS 1800
Lecture 20
Fluids and Pressure
Introduction
Section 0
Lecture 1
Slide 3
Introduction
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Fluids and Pressure
Lecture 20 Slide 3
Dennison’s Laws of Fluids
• When push comes to shove, fluids are just like
other stuff.
• Pascal’s Principle: Pressure extends uniformly in all
directions in a fluid.
• Boyle’s Law: Work on a fluid equals PΔV
• Bernoulli’s Principle: Conservation of energy for fluids
Introduction
Section 0
Lecture 1
Slide 4
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Fluids and Pressure
Lecture 20 Slide 4
Physics of Technology
PHYS 1800
Lecture 20
Fluids and Pressure
Introduction
Section 0
Lecture 1
Slide 5
Hydraulics:
A Simple Machine with Fluids
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Fluids and Pressure
Lecture 20 Slide 5
How does a
hydraulic jack
work?
•
•
•
•
•
•
A force applied to a piston with a small area can produce a large increase in
pressure in the fluid because of the small area of the piston.
This increase in pressure is transmitted through the fluid to the piston with
the larger area (Pascal’s Principle).
The force exerted on the larger piston is proportional to the area of the
piston: F = PA.
Applying the same pressure to the larger area of the second piston results in
a larger force on the second piston.
Introduction
0 Lecture
1 Slide of
6 energy says
But this
comes atSection
a price.
Conservation
work in must equal work out
that is ΔW=F Δd = (P A) Δd = P ΔV , so Δd1 > Δd2
AnotherINTRODUCTION
way to think
this
TO Modern of
Physics
PHYX is
2710 conservation of stuff: Vin = Vout
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Fluids and Pressure
Lecture 20 Slide 6
A force of 10 N is
applied to a circular
piston with an area of
2 cm2 in a hydraulic
jack. The output
piston for the jack has
an area of 100 cm2.
What is the pressure in
the fluid?
a)
b)
c)
d)
0.002 Pa
5 Pa
10 Pa
Introduction
50 kPa
F1 = 10 N
A1 = 2 cm2 = 0.0002 m2
Section 0
P = F1 / A1 = 10 N / 0.0002 m2
Lecture 1 Slide 7
= 50,000 N/m2
= 50 kPa
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Fluids and Pressure
Lecture 20 Slide 7
What is the force
exerted on the output
piston by the fluid?
a)
b)
c)
d)
50 N
500 N
5,000 N
Introduction
50,000 N
P = 50 kPa
A2 = 100 cm2 = 0.01 m2
F = PA = Slide
(50,000
N/m2)(0.01 m2)
8
The mechanical advantage is
500 N / 10 N = 50.
Section 0 1 Lecture 11
= 500 N
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Fluids and Pressure
Lecture 20 Slide 8
Hydraulic Devices
Introduction
Section 0
Lecture 1
Slide 9
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Fluids and Pressure
Lecture 20 Slide 9
Hydraulic Brakes
Introduction
Section 0
Lecture 1
Slide 10
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Fluids and Pressure
Lecture 20 Slide 10
Physics of Technology
PHYS 1800
Lecture 20
Fluids and Pressure
Introduction
Section 0
Lecture 1
Slide 11
Barometers and Atmospheric Pressure
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Fluids and Pressure
Lecture 20 Slide 11
Atmospheric Pressure and the Behavior of Gases
• Living on the surface of the earth, we are at the
bottom of a sea of air.
• This sea of air is thinner at higher altitudes.
• It is also thinner during certain weather conditions.
• We describe this property by atmospheric pressure:
the pressure of the layer of air that surrounds the
earth.
– At sea level, the atmospheric pressure is 100 kPa, or
14.7 pounds per square inch, but it decreases with
altitude.
Introduction
Section 0
Lecture 1
Slide 12
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Fluids and Pressure
Lecture 20 Slide 12
The Barometer
• Torricelli invented the barometer, a device
for measuring atmospheric pressure, in an
attempt to explain why water pumps could
pump water to a height of only 32 feet.
• He filled a tube with mercury and inverted it
into an open container of mercury.
• Mercury worked well because it is much
denser than water.
– Density is the mass of an object divided by
its volume.
• Air pressure acting on the mercury in the
dish supported
a column of mercury, of
Introduction Section 0 Lecture 1 Slide 13
height proportional to the atmospheric
pressure.
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Fluids and Pressure
Lecture 20 Slide 13
Making Physics Pay Big Bucks
• Otto von Guericke performed a famous experiment to demonstrate the
effects of air pressure.
• He designed two bronze hemispheres that could be smoothly joined
together at their rims.
• He pumped the air out of the
sphere formed from the
two hemispheres.
• Two eight-horse
teams were
unable
Introduction Section 0
to pull the
hemispheres apart.
Lecture 1
Slide 14
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Fluids and Pressure
Lecture 20 Slide 14
• In other experiments on variations in atmospheric
pressure, Pascal sent his brother-in-law to the top of a
mountain with a barometer and a partially inflated
balloon.
• The balloon expanded as
the climbers gained elevation.
• This was evidence of a
decrease in the external
atmospheric pressure.
Introduction
Section 0
Lecture 1
Slide 15
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Fluids and Pressure
Lecture 20 Slide 15
Boyle’s Law
• Variations in the
volume and density of
a gas that
accompanies changes
in pressure were
studied by Boyle and
Mariotte.
• The density of a
column of air
decreases as altitude
increases
because
Introduction
Section 0 air
Lecture 1
expands as pressure
decreases.
Slide 16
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Fluids and Pressure
Lecture 20 Slide 16
Application of Avagadro’s NUmber
Introduction
Section 0
Lecture 1
Slide 17
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Fluids and Pressure
Lecture 20 Slide 17
Application of Avagadro’s NUmber
Introduction
Section 0
Lecture 1
Slide 18
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Fluids and Pressure
Lecture 20 Slide 18
Boyle’s Law
• Boyle discovered that the
volume of a gas is inversely
proportional to the pressure.
• Boyle’s Law: PV = constant
• If the pressure increases, the
volume decreases.
• The density of a column of air
decreases as altitude
increases because air
expands as pressure
Introduction Section 0 Lecture 1 Slide 19
decreases.
• P1V1 = P2V2
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Fluids and Pressure
Lecture 20 Slide 19
A fixed quantity of gas is held in a cylinder capped at one end by a
movable piston. The pressure of the gas is initially 1 atmosphere
(101 kPa) and the volume is initially 0.3 m3. What is the final
volume of the gas if the pressure is increased to 3 atmospheres at
constant temperature?
P1 = 1 atm
V1 = 0.3 m3
a)
0.1 m3
b)
0.3 m3
c)
d)
1 m3Introduction
3 m3
Section 0
Physics of Technology—PHYS 1800
Spring 2009
V2 =Slide
P120
V1 / P2
= (1 atm)(0.3 m3) / 3 atm
= 0.1 m3
Lecture 1
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
P2 = 3 atm
V2 = ?
Fluids and Pressure
Lecture 20 Slide 20
Range of
Pressures
Introduction
Section 0
Lecture 1
Slide 21
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Fluids and Pressure
Lecture 20 Slide 21
Barometers
Introduction
Section 0
Lecture 1
Slide 22
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Fluids and Pressure
Lecture 20 Slide 22
Pressure Gauges
Introduction
Section 0
Lecture 1
Slide 23
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Fluids and Pressure
Lecture 20 Slide 23
Capacitance Manometer
Introduction
Section 0
Lecture 1
Slide 24
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Fluids and Pressure
Lecture 20 Slide 24
Convection Pressure Gauges
Introduction
Section 0
Lecture 1
Slide 25
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Fluids and Pressure
Lecture 20 Slide 25
Introduction
Section 0
Lecture 1
Slide 26
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Fluids and Pressure
Lecture 20 Slide 26
Physics of Technology
PHYS 1800
Lecture 20
Fluids and Pressure
Introduction
Section 0
Lecture 1
Slide 27
Archimedes's Principle:
Buoyant Forces
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Fluids and Pressure
Lecture 20 Slide 27
Archimedes’ Principle
• The average density of an object compared to a fluid determines
whether the object will sink or float in that liquid.
• The upward force that pushes objects back toward the surface in
liquids is called the buoyant force.
• Archimedes’ Principle: The buoyant force acting on an object
fully or partially submerged in a fluid is equal to the weight of the
fluid displaced by the object.
Introduction
Section 0
Lecture 1
Slide 28
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Fluids and Pressure
Lecture 20 Slide 28
Introduction
Section 0
Lecture 1
Slide 29
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Fluids and Pressure
Lecture 20 Slide 29
Archimedes’ Principle
•
For example, consider a block submerged in water, suspended from a string.
– The pressure of the water pushes on the block from all sides.
– Because the pressure increases with depth, the pressure at the bottom of the block
is greater than at the top.
– There is a larger force (F = PA) pushing up at the bottom than there is pushing
down at the top.
– The difference between these two forces is the buoyant force.
The buoyant force is proportional to both
the height and the cross-sectional area of
the block, and thus to its volume.
Introduction
Section 0
The volume of the fluid displaced is
directly related to the weight of the fluid
displaced.
Lecture
1 Slide 30
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Weight  mg  Vdg
Volume  Ah
Excess Pressure P 
W dgAh

 dgh
A
a
Fluids and Pressure
Lecture 20 Slide 30
Physics of Technology
Next Lab/Demo:
Rotational Motion
Fluids
Thursday 1:30-2:45
ESLC 46
Ch 8 and 9
Next Class:
Wednesday 10:30-11:20
BUS
Slide 31318 room
Review Ch 9
Introduction
Section 0
Lecture 1
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Fluids and Pressure
Lecture 20 Slide 31