11/07/2013PHY 113 C Fall Lecture 201 PHY 113 C General Physics I 11 AM - 12:15 PM TR Olin 101 Plan for Lecture 20: Chapter 19: The notion of temperature 1.Review of fluid physics 2.Temperature equilibrium 3.Temperature scales 4.Temperature in ideal gases

11/07/2013 PHY 113 C Fall Lecture 202

11/07/2013PHY 113 C Fall Lecture 203 The physics of fluids. Fluids include liquids (usually “incompressible) and gases (highly “compressible”). Fluids obey Newton’s equations of motion, but because they move within their containers, the application of Newton’s laws to fluids introduces some new forms.  Pressure: P=force/area 1 (N/m 2 ) = 1 Pascal  Density:  =mass/volume 1 kg/m 3 = gm/ml Review:

11/07/2013PHY 113 C Fall Lecture 204 Review of equations describing static fluids in terms of pressure P and density  Note that for compressible fluids (such as air), the relationship between pressure and density is more complicated. Buoyant force for fluid acting on a solid – net force due to volume V displaced being displaced in fluid: F B =  fluid V displaced g

11/07/2013PHY 113 C Fall Lecture 205 Bernoulli’s equation:

11/07/2013PHY 113 C Fall Lecture 206 Webassign questions on fluids (Assignment #17) A large man sits on a four-legged chair with his feet off the floor. The combined mass of the man and chair is 95.0 kg. If the chair legs are circular and have a radius of cm at the bottom, what pressure does each leg exert on the floor? mg mg/4 P=F/A=(mg/4)/A

11/07/2013PHY 113 C Fall Lecture 207 Webassign questions on fluids (Assignment #17) A swimming pool has dimensions 32.0 m ✕ 7.0 m and a flat bottom. The pool is filled to a depth of 2.50 m with fresh water. (a) What is the force exerted by the water on the bottom? (b) What is the force exerted by the water on each end? (The ends are 7.0 m.) (c) What is the force exerted by the water on each side? (The sides are 32.0 m.)

11/07/2013PHY 113 C Fall Lecture 208 Webassign questions on fluids (Assignment #17) A swimming pool has dimensions 32.0 m ✕ 7.0 m and a flat bottom. The pool is filled to a depth of 2.50 m with fresh water. (a) What is the force exerted by the water on the bottom? h=2.5m F bottom =PA=  ghA

11/07/2013PHY 113 C Fall Lecture 209 Webassign questions on fluids (Assignment #17) A swimming pool has dimensions 32.0 m ✕ 7.0 m and a flat bottom. The pool is filled to a depth of 2.50 m with fresh water. (b) What is the force exerted by the water on each end? (The ends are 7.0 m.) h=2.5m w=7.0m

11/07/2013PHY 113 C Fall Lecture 2010 Webassign questions on fluids (Assignment #17)

11/07/2013PHY 113 C Fall Lecture 2011 yy zz

11/07/2013PHY 113 C Fall Lecture 2012

11/07/2013PHY 113 C Fall Lecture 2013 Webassign questions on fluids (Assignment #17) The gravitational force exerted on a solid object is 5.30 N. When the object is suspended from a spring scale and submerged in water, the scale reads 3.50 N (figure). Find the density of the object.

11/07/2013PHY 113 C Fall Lecture 2014 Webassign questions on fluids (Assignment #17) A light balloon is filled with 373 m 3 of helium at atmospheric pressure. (a) At 0°C, the balloon can lift a payload of what mass? Note:  air = 2.9 kg/m 3 :  He = kg/m 3

11/07/2013PHY 113 C Fall Lecture 2015 Webassign questions on fluids (Assignment #17) A hypodermic syringe contains a medicine with the density of water (see figure below). The barrel of the syringe has a cross- sectional area A = m 2, and the needle has a cross- sectional area a = m 2. In the absence of a force on the plunger, the pressure everywhere is 1.00 atm. A force of magnitude 2.65 N acts on the plunger, making medicine squirt horizontally from the needle. Determine the speed of the medicine as it leaves the needle's tip.

11/07/2013PHY 113 C Fall Lecture 2016 Dictionary definition: temperature – a measure of the the warmth or coldness of an object or substance with reference to some standard value. The temperature of two systems is the same when the systems are in thermal equilibrium. “Zeroth” law of thermodynamics: If objects A and B are separately in thermal equilibrium with a third object C, then objects A and B are in thermal equilibrium with each other. T 1 T2T2 T3T3 Not equilibrium: Equilibrium:

11/07/2013PHY 113 C Fall Lecture 2017 Constant temperature “bath” T T At equilibrium:

11/07/2013PHY 113 C Fall Lecture 2018 Temperature scales T F =9/5 T C + 32 Kelvin scale: T = T C o T 

11/07/2013PHY 113 C Fall Lecture 2019 iclicker question: Suppose you find yourself in a hotel in Europe or Canada. Which Celsius temperature would you set the thermostat for comfort? A.-20 o C B.+20 o C C.+40 o C D.+60 o C E.+80 o C

11/07/2013PHY 113 C Fall Lecture 2020 There is a lowest temperature: T 0 = o C = 0 K Kelvin (“absolute temperature”) scale T C = T K Example – Room temperature = 68 o F = 20 o C = K

11/07/2013PHY 113 C Fall Lecture 2021

11/07/2013PHY 113 C Fall Lecture 2022 Effects of temperature on matter Solids and liquids L i (equilibrium bond length at T i ) Model of a solid composed of atoms and bonds LL Thermal exansion:  L =  L i  T

11/07/2013PHY 113 C Fall Lecture 2023 Typical expansion coefficients at T C = 20 o C: Linear expansion:  L =  L i  T Steel:  = 11 x / o C Concrete:  = 12 x / o C Volume expansion: V=L 3   V = 3  V i  T =  V i  T Alcohol:  = 1.12 x / o C Air:  = 3.41 x / o C

11/07/2013PHY 113 C Fall Lecture 2024 iclicker question On the last slide – we suggest that  =3 . Is this result A.One of those mysteries of physics that has no explanation? B.A result that we can derive? L L+  L V=L 3  V+  V=(L+  L) 3  V(1+3(  L/L))

11/07/2013PHY 113 C Fall Lecture 2025

11/07/2013PHY 113 C Fall Lecture 2026 Brass Steel

11/07/2013PHY 113 C Fall Lecture 2027 Switch in thermostat Modern thermostats use electrical circuits to detect temperature

11/07/2013PHY 113 C Fall Lecture 2028 Effects of temperature on materials – continued strange case of water:

11/07/2013PHY 113 C Fall Lecture 2029 Effects of temperature on materials – continued -- ideal gas “law” (thanks to Robert Boyle ( ), Jacques Charles ( ), and Gay- Lussac ( ) pressure in Pascals volume in m 3 # of moles temperature in K J/(mol K) 1 mole corresponds to x molecules

11/07/2013PHY 113 C Fall Lecture 2030 P 0 =12.6 atm T 0 =27.5 o C n 0 P=? T=81.0 o C n=n 0 /3

11/07/2013PHY 113 C Fall Lecture 2031 Assuming that air behaves like an ideal gas, what is the density of air at T=0 o C and P=1 atm?

11/07/2013PHY 113 C Fall Lecture 2032 Typical composition of air: url: