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Welcome Physics 202 Professor Lee Carkner Lecture 1
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Questions to Consider Am I in the right place? Physics 202: Basic Physics Do I have the right stuff? Halliday, Resnick, and Walker, 6 th Edition Lab manual Calculator WebAssign Card
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Things to Know Professor Dr. Lee Carkner Office Hours MWF 11:15-12:15 (after class) Science 208 Help session: TBA Lab section See me after class to change No lab this week
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How Does the Class Work? Read the book material before class Do the exercises through WebAssign Come to class Do the PAL discussion questions Come to discussion and do the discussion exercises Lab once a week Two tests and final
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Web Page http://helios.augustana.edu/~lc/ph202 Outline gives homework and readings Lectures posted online before class Download and bring to class, fill in blanks
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Grading Exams (2): 30% (15% each) Final: 20% Lab: 20% Discussion: 10% Pre-class Homework: 10% In-class PAL: 10%
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PAL What is PAL? Physics Active Learning Each class you will get a PAL worksheet Contains questions about the material and feedback opportunities Worth 10% of your grade Need to do readings and come to class Can drop (or skip) three PAL’s “Physics is your PAL!”
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Guidelines for Work Handed In Written answers must be in complete sentences Numbers must have units Answers must reasonable If not reasonable, explain why All work must be neat and easily readable
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WebAssign Homework will be entered and graded online At webassign.com Click on student login Username is your first and last name together (as in your augustana email) Institution is “augustana” Password is your augustana student ID number You can change this After login, click on the current assignment and complete it WARNING: Can only submit it once I will post a tutorial later today
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What is Physics? Phys"ics (?), n. The science of nature, or of natural objects; that branch of science which treats of the laws and properties of matter, and the forces acting upon it; especially, that department of natural science which treats of the causes (as gravitation, heat, light, magnetism, electricity, etc.) that modify the general properties of bodies; natural philosophy. --Webster’s Dictionary 1913
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What is Physics? Physics is a way of figuring out how things work More specifically: what are the underlying rules that govern how things work? We will deal mostly with classical physics: i.e. How did things work before 1900?
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Why Take Physics? You may need to know how things work You can learn how to: Use reason and logic Solve problems Use mathematics It is useful to understand how we know how things work
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Course Outline Fluids Ch. 15 OscillationsCh. 16 Waves ICh. 17 Waves IICh. 18 First Exam 1 st Law of ThermodynamicsCh. 19 Kinetic Theory of GasesCh. 20 2 nd Law of ThermodynamicsCh. 21 Second Exam Electromagnetic WavesCh. 34 ImagesCh. 35 InterferenceCh. 36 DiffractionCh. 37 Final Exam
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Fluids A fluid is a substance that can flow A liquid or a gas A fluid has no internal structure Since a fluid can flow, any individual piece of the fluid can be hard to keep track of Mass and force are often not useful The important quantities of a fluid are density and pressure
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Density The density ( ) of a fluid is the mass per unit volume for an arbitrary volume element Density can vary with temperature or pressure Liquids are much less compressible than gases The SI unit of density is kg/m 3 Air ~1.21 kg/m 3 Water ~1000 kg/m 3 Rock ~3000 kg/m 3 Metal ~8000 kg/m 3
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Pressure Pressure is defined as the force per unit area P= F/ A The SI unit of pressure is the pascal (Pa), a newton per square meter An important practical unit of pressure is the atmosphere, the pressure of the Earth’s atmosphere at sea level 1 atm = 1.01 X 10 5 Pa = 14.7 psi
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Fluids and Gravity We will normally deal with fluids in a gravitational field Fluids in the absence of gravity will form a sphere Fluids on a planet will exert a pressure which increases with depth For a fluid that exerts a pressure due to gravity: P= gh Where h is the height of the fluid in question, and g is the acceleration of gravity
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Gauge Pressure If the fluid has additional material pressing down on top of it (e.g. the atmosphere above a column of water) then the equation should read: P=p 0 + gh Pressure usually depends only on the height of the fluid column The gh part of the equation is called the gauge pressure A tire gauge that shows a pressure of “0” is really measuring a pressure of one atmosphere
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Measuring Pressure If you have a U-shaped tube with some liquid in it and apply a pressure to one end, the height of the fluid in the other arm will increase Since the pressure of a fluid depends only on its height, this set-up can be used to measure pressure This describes an open tube manometer Since air is pressing down on the open end, the manometer actually measures gauge pressure above air pressure or overpressure If you close off one end of the tube and keep it in vacuum, the air pressure on the open end will cause the fluid to rise This is called a barometer Measures atmospheric pressure
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Barometers
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Pascal’s Principle Pressure applied to an enclosed fluid is transmitted to every portion of the fluid and the container Pascal’s principle is the basis for the hydraulic lever Consider our U-shaped tube: If you apply a pressure at one end, the same pressure is felt at the other end But what if the other end of the tube is thicker?
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A Hydraulic Jack
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Hydraulic Jack Since the pressures are the same and the areas are different, the force on the other end is larger (from P=F/A) But work must be conserved: W=Fd, so if the force is greater at the other end the displacement must be less A person can lift a car with a hydraulic jack, but ratcheting the jack 3 feet may only move the car an inch
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Next Time Discussion tomorrow Read 15.1-15.6 (today’s lecture reading) for tomorrow No lab this week Check WebAssign for Wednesday’s homework Due before 10 am Wednesday!!
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