fluids and pressure introduction section 0 lecture 1 slide 1 lecture 20 slide 1 introduction to...
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Fluids and Pressure
Introduction Section 0 Lecture 1 Slide 1
Lecture 20 Slide 1
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Physics of Technology
PHYS 1800
Lecture 20
Fluids and Pressure
Fluids and Pressure
Introduction Section 0 Lecture 1 Slide 2
Lecture 20 Slide 2
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
PHYSICS OF TECHNOLOGY Spring 2009 Assignment Sheet
*Homework Handout
PHYSICS OF TECHNOLOGY - PHYS 1800 ASSIGNMENT SHEET
Spring 2009 Date Day Lecture Chapter Homework Due Feb 16 17 18 19 20
M Tu W H F*
Presidents Day Angular Momentum (Virtual Monday) Review Test 2 Static Fluids, Pressure
No Class 8 5-8 5-8 9
-
Feb 23 25 27
M W F*
Flotation Fluids in Motion Temperature and Heat
9 9 10
6
Mar 2 4 6
M W F*
First Law of Thermodynamics Heat flow and Greenhouse Effect Climate Change
10 10 -
7
Mar 9-13 M-F Spring Break No Classes Mar 16 18 20
M W F*
Heat Engines Power and Refrigeration Electric Charge
11 11 12
8
Mar 23 25 26 27
M W H F*
Electric Fields and Electric Potential Review Test 3 Electric Circuits
12 13 9-12 13
-
Mar 30 Apr 1 3
M W F
Magnetic Force Review Electromagnets Motors and Generators
14 9-12 14
9
Apr 6 8 10
M W F*
Making Waves Sound Waves E-M Waves, Light and Color
15 15 16
10
Apr 13 15 17
M W F*
Mirrors and Reflections Refraction and Lenses Telescopes and Microscopes
17 17 17
11
Apr 20 22 24
M W F
Review Seeing Atoms The really BIG & the really small
1-17 18 (not on test) 21 (not on test)
No test week 12
May 1 F Final Exam: 09:30-11:20am * = Homework Handout
Fluids and Pressure
Introduction Section 0 Lecture 1 Slide 3
Lecture 20 Slide 3
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Physics of Technology
PHYS 1800
Lecture 20
Fluids and Pressure
Introduction
Fluids and Pressure
Introduction Section 0 Lecture 1 Slide 4
Lecture 20 Slide 4
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
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
Fluids and Pressure
Introduction Section 0 Lecture 1 Slide 5
Lecture 20 Slide 5
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Physics of Technology
PHYS 1800
Lecture 20
Fluids and Pressure
Hydraulics: A Simple Machine with Fluids
Fluids and Pressure
Introduction Section 0 Lecture 1 Slide 6
Lecture 20 Slide 6
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
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.
• But this comes at a price. Conservation of energy says work in must equal work out that is ΔW=F Δd = (P A) Δd = P ΔV , so Δd1 > Δd2 • Another way to think of this is conservation of stuff: Vin = Vout
Fluids and Pressure
Introduction Section 0 Lecture 1 Slide 7
Lecture 20 Slide 7
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
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) 0.002 Pab) 5 Pac) 10 Pad) 50 kPa
F1 = 10 NA1 = 2 cm2 = 0.0002 m2
P = F1 / A1 = 10 N / 0.0002 m2
= 50,000 N/m2 = 50 kPa
Fluids and Pressure
Introduction Section 0 Lecture 1 Slide 8
Lecture 20 Slide 8
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
What is the force exerted on the
output piston by the fluid?
a) 50 Nb) 500 Nc) 5,000 Nd) 50,000 N
P = 50 kPaA2 = 100 cm2 = 0.01 m2
F1 = PA1 = (50,000 N/m2)(0.01 m2) = 500 NThe mechanical advantage is 500 N / 10 N = 50.
Fluids and Pressure
Introduction Section 0 Lecture 1 Slide 9
Lecture 20 Slide 9
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Hydraulic Devices
Fluids and Pressure
Introduction Section 0 Lecture 1 Slide 10
Lecture 20 Slide 10
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Hydraulic Brakes
Fluids and Pressure
Introduction Section 0 Lecture 1 Slide 11
Lecture 20 Slide 11
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Physics of Technology
PHYS 1800
Lecture 20
Fluids and Pressure
Barometers and Atmospheric Pressure
Fluids and Pressure
Introduction Section 0 Lecture 1 Slide 12
Lecture 20 Slide 12
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
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.
Fluids and Pressure
Introduction Section 0 Lecture 1 Slide 13
Lecture 20 Slide 13
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
• 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 height proportional to the atmospheric pressure.
The Barometer
Fluids and Pressure
Introduction Section 0 Lecture 1 Slide 14
Lecture 20 Slide 14
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
• 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 to pull the hemispheres apart.
Making Physics Pay Big Bucks
Fluids and Pressure
Introduction Section 0 Lecture 1 Slide 15
Lecture 20 Slide 15
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
• 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.
Fluids and Pressure
Introduction Section 0 Lecture 1 Slide 16
Lecture 20 Slide 16
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
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 air expands as pressure decreases.
Fluids and Pressure
Introduction Section 0 Lecture 1 Slide 17
Lecture 20 Slide 17
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Application of Avagadro’s NUmber
Fluids and Pressure
Introduction Section 0 Lecture 1 Slide 18
Lecture 20 Slide 18
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Application of Avagadro’s NUmber
Fluids and Pressure
Introduction Section 0 Lecture 1 Slide 19
Lecture 20 Slide 19
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
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 decreases.
• P1V1 = P2V2
Fluids and Pressure
Introduction Section 0 Lecture 1 Slide 20
Lecture 20 Slide 20
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
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?
a) 0.1 m3
b) 0.3 m3
c) 1 m3
d) 3 m3
P1 = 1 atm P2 = 3 atm V1 = 0.3 m3 V2 = ?
V2 = P1V1 / P2 = (1 atm)(0.3 m3) / 3 atm = 0.1 m3
Fluids and Pressure
Introduction Section 0 Lecture 1 Slide 21
Lecture 20 Slide 21
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Range of Pressures
Fluids and Pressure
Introduction Section 0 Lecture 1 Slide 22
Lecture 20 Slide 22
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Barometers
Fluids and Pressure
Introduction Section 0 Lecture 1 Slide 23
Lecture 20 Slide 23
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Pressure Gauges
Fluids and Pressure
Introduction Section 0 Lecture 1 Slide 24
Lecture 20 Slide 24
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Capacitance Manometer
Fluids and Pressure
Introduction Section 0 Lecture 1 Slide 25
Lecture 20 Slide 25
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Convection Pressure Gauges
Fluids and Pressure
Introduction Section 0 Lecture 1 Slide 26
Lecture 20 Slide 26
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Fluids and Pressure
Introduction Section 0 Lecture 1 Slide 27
Lecture 20 Slide 27
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Physics of Technology
PHYS 1800
Lecture 20
Fluids and Pressure
Archimedes's Principle:Buoyant Forces
Fluids and Pressure
Introduction Section 0 Lecture 1 Slide 28
Lecture 20 Slide 28
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
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.
Fluids and Pressure
Introduction Section 0 Lecture 1 Slide 29
Lecture 20 Slide 29
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Fluids and Pressure
Introduction Section 0 Lecture 1 Slide 30
Lecture 20 Slide 30
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
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.
The volume of the fluid displaced is directly related to the weight of the fluid displaced.
Weight mg VdgVolume Ah
Excess Pressure P W
A
dgAh
adgh
Fluids and Pressure
Introduction Section 0 Lecture 1 Slide 31
Lecture 20 Slide 31
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Physics of Technology
Next Lab/Demo: Rotational Motion
FluidsThursday 1:30-2:45
ESLC 46 Ch 8 and 9
Next Class: Wednesday 10:30-11:20
BUS 318 roomReview Ch 9