Physics 207: Lecture 20, Pg 1Physics 207,Physics 207, Lecture 20, NovLecture 20, Nov 11 11 ‘‘0909TODAY:TODAY:FluidsFluidsOscillationsOscillations Simple Harmonic Motion Simple Harmonic Motion ResonanceResonanceASSIGNMENTS:ASSIGNMENTS:Read Read Chaper Chaper 15 15 ‘‘FluidsFluids’’Lab thisLab this week - SHM and Resonanceweek - SHM and ResonanceNext weekNext week’’s labs lab on Modeling - do the on Modeling - do the ‘‘prelabprelab’’ atathome firsthome first‘‘How Physics lets us image the human brainHow Physics lets us image the human brain’’Prof. Beth Prof. Beth MeyerandMeyerand,, UW Dept Medical PhysicsUW Dept Medical PhysicsFridayFriday Honors Lecture (optional)Honors Lecture (optional)Physics 207: Lecture 20, Pg 2What about the What about the ‘‘phase constantphase constant’’??In a plot of x(t) = A cos(ωt + θ) versus time, t, in whichdirection does the curve ‘shift’ compared to θ = 0?A. To the left (toward negative t)B. To the right (toward positive t)C. No shiftPhysics 207: Lecture 20, Pg 3Simple Harmonic Oscillator: Initial ConditionsSimple Harmonic Oscillator: Initial ConditionsLast time we found the general solution for the position of amass on a spring is x(t) = A cos(ωt + θ).Now suppose we start the spring at t = 0 at x = 0 and v = Vi.What is x(t)? (That is, what are the constants A and θ ?)A. Vi cos(ωt)B. 0C. ωVi sin(ωt)D. -(Vi/ω)cos(ωt + π/2)Physics 207: Lecture 20, Pg 6Physics 207: Lecture 20, Pg 7Physics 207: Lecture 20, Pg 8Physics 207: Lecture 20, Pg 9Physics 207: Lecture 20, Pg 10Physics 207: Lecture 20, Pg 11Physics 207: Lecture 20, Pg 12Physics 207: Lecture 20, Pg 18FluidsFluidsAgenda: Fluids and Elasticity (Ch.15) Density PressurePhysics 207: Lecture 20, Pg 19Physics 207: Lecture 20, Pg 20Physics 207: Lecture 20, Pg 21Physics 207: Lecture 20, Pg 22About how much does 1About how much does 1 gallon ofgallon of water weigh?water weigh?A. 2.2 lbsB. 4.4 lbsC. 6.6 lbsD. 8.6 lbsE. 10.1 lbsPhysics 207: Lecture 20, Pg 23Which weighs more?Which weighs more?A. The air in the kitchen ‘fridgeB. An orangePhysics 207: Lecture 20, Pg 24PressurePressureA fluid in a container presses with an outward forceagainst the walls of that container. The pressure isdefined as the ratio of the force to the area on which theforce is exerted.The SI units of pressure are N/m2, also defined as thepascal, where 1 pascal = 1 Pa = 1 N/m2.Physics 207: Lecture 20, Pg 25Physics 207: Lecture 20, Pg 26Atmospheric PressureAtmospheric PressureThe global average sea-level pressure is 101,300 Pa.Consequently we define the standard atmosphere as1 Pa = 1 N/m2Physics 207: Lecture 20, Pg 27Pressure in LiquidsPressure in LiquidsThe pressure at depth d in a liquid iswhere ρ isyou will prove this for HW this week…. theliquid’s density, and p0 is the pressure at the surface of theliquid. Because the fluid is at rest, the pressure is calledthe hydrostatic pressure. The fact that g appears in theequation reminds us that there is a gravitationalcontribution to the pressure.Physics 207: Lecture 20, Pg 28WhatWhat’’s the pressure at thes the pressure at thebottom of a diving well at depthbottom of a diving well at depth= 10 m?= 10 m?A. 1 atmB. 2 atmC. 3 atmD. 10
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