康涅狄格州大学：《普通物理》课程PPT教学课件（英文版）Lecture 24 Announcements

Physics 121: Lecture 24 Today's Agenda Announcements About midterm 2: next Tuesday Covers Chap 6-13 Homework 10: due Friday Dec 2@ 6: 00 PM Chap.10:#2,22,24,28,34,42,49,55,and58 Chap.11:#2,9,13,27,30,34,and43 Today's topiCs Temperature and zeroth law of thermodynamics Temperature scales and thermal expansion Ideal gas Heat and energy Laws of thermodynamics Physics 121: Lecture 24, Pg

Physics 121: Lecture 24, Pg 1 Physics 121: Lecture 24 Today’s Agenda Announcements About midterm 2: next Tuesday Covers Chap. 6 - 13. Homework 10: due Friday Dec. 2 @ 6:00 PM. Chap. 10: # 2, 22, 24, 28, 34, 42, 49, 55, and 58. Chap. 11: # 2, 9, 13, 27, 30, 34, and 43. Today’s topics Temperature and Zeroth Law of Thermodynamics Temperature scales and thermal expansion Ideal gas Heat and energy Laws of thermodynamics

Chap. 13: Temperature Temperature: measure of the motion of the individual atoms and molecules in a gas liquid or solid related to average kinetic energy of constituents High temperature: constituents are moving around energetically In a gas at high temperature the individual gas molecules are moving about independently at high speeds In a solid at high temperature the individual atoms of the solid are vibrating energetically in place The converse is true for a"cold"object In a gas at low temperature the individual gas molecules are moving about sluggishly There is an absolute zero temperature at which the motions of atoms and molecules practically stop There is an absolute zero temperature at which the classical motions of atoms and molecules practically stop Physics 121: Lecture 24, Pg 2

Physics 121: Lecture 24, Pg 2 Chap. 13: Temperature Temperature: measure of the motion of the individual atoms and molecules in a gas, liquid, or solid. related to average kinetic energy of constituents High temperature: constituents are moving around energetically In a gas at high temperature the individual gas molecules are moving about independently at high speeds. In a solid at high temperature the individual atoms of the solid are vibrating energetically in place. The converse is true for a "cold" object. In a gas at low temperature the individual gas molecules are moving about sluggishly. There is an absolute zero temperature at which the motions of atoms and molecules practically stop. There is an absolute zero temperature at which the classical motions of atoms and molecules practically stop

Heat Solids, liquids or gases have internal energy Kinetic energy from random motion of molecules translation rotation vibration At equilibrium, it is related to temperature Heat: transfer of energy from one object to another as a result of their different temperatures Thermal contact: energy can flow between objects Physics 121: Lecture 24, Pg 3

Physics 121: Lecture 24, Pg 3 Heat Solids, liquids or gases have internal energy Kinetic energy from random motion of molecules translation, rotation, vibration At equilibrium, it is related to temperature Heat: transfer of energy from one object to another as a result of their different temperatures Thermal contact: energy can flow between objects T1 T2 U1 U2 >

Zeroth Law of Thermodynamics Thermal equilibriun when objects in thermal contact cease U heat transfer same temperature 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 C A B Physics 121: Lecture 24, Pg 4

Physics 121: Lecture 24, Pg 4 Zeroth Law of Thermodynamics Thermal equilibrium: when objects in thermal contact cease heat transfer same temperature T1 T2 U1 U2 = 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. A C B

Temperature scales Three main scales Farenheit Celcius Kelvin 212 100 373. 10.Water boils 32 0 273.15 Water freezes 459.67 273.15 0 ------- Absolute zero Physics 121: Lecture 24, Pg 5

Physics 121: Lecture 24, Pg 5 Temperature scales Three main scales 212 Farenheit 100 Celcius 32 0 273.15 373.15 Kelvin Water boils Water freezes -459.67 -273.15 0 Absolute Zero

Some interesting facts T(K 10 Hydrogen bomb In 1724. Gabriel Fahrenheit made thermometers using mercury. The zero point of his scale is 10 Sun's interior attained by mixing equal parts of water, ice, and salt. a second point was obtained when pure 10 Solar corona water froze(originally set at 300F), and a third (set at 96 F)"when placing the thermometer in 105 the mouth of a healthy man On that scale, water boiled at 212 10 →Sun' s surface Later, Fahrenheit moved the freezing point of 10 water to 32 so that the scale had 180 1 Copper melts increments) 100 Water freezes In 1745. Carolus Linnaeus of Upsula, Sweden Liquid nitrogen described a scale in which the freezing point of water was zero, and the boiling point 100, Liquid hydrogen making it a centigrade(one hundred steps Liquid helium scale. Anders Celsius(1701-1744)used the reverse scale in which 100 represented the 0.1 freezing point and zero the boiling point of water, still, of course, with 100 degrees between the two Lowest T defining points 109K Physics 121: Lecture 24, Pg 6

Physics 121: Lecture 24, Pg 6 Some interesting facts In 1724, Gabriel Fahrenheit made thermometers using mercury. The zero point of his scale is attained by mixing equal parts of water, ice, and salt. A second point was obtained when pure water froze (originally set at 30oF), and a third (set at 96oF) “when placing the thermometer in the mouth of a healthy man”. On that scale, water boiled at 212. Later, Fahrenheit moved the freezing point of water to 32 (so that the scale had 180 increments). In 1745, Carolus Linnaeus of Upsula, Sweden, described a scale in which the freezing point of water was zero, and the boiling point 100, making it a centigrade (one hundred steps) scale. Anders Celsius (1701-1744) used the reverse scale in which 100 represented the freezing point and zero the boiling point of water, still, of course, with 100 degrees between the two defining points. T (K) 108 107 106 105 104 103 100 10 1 0.1 Hydrogen bomb Sun’s interior Solar corona Sun’s surface Copper melts Water freezes Liquid nitrogen Liquid hydrogen Liquid helium Lowest T ~ 10-9K

Thermal expansion In most liquids or solids, when temperature rises molecules have more kinetic energy > they are moving faster, on the average consequently, things tend to expand amount of expansion AL depends on change in temperature at original length Lo coefficient of thermal expansion 》Lo+△L=Lo+aLo△T 》△L=aLo△T( linear expansion) △V=阝Lo△T( olume expansion) V ∨+△V Physics 121: Lecture 24, Pg7

Physics 121: Lecture 24, Pg 7 Thermal expansion In most liquids or solids, when temperature rises molecules have more kinetic energy »they are moving faster, on the average consequently, things tend to expand amount of expansion L depends on… change in temperature T original length L0 coefficient of thermal expansion »L0 + L = L0 +  L0 T »L =  L0 T (linear expansion) »V =  L0 T (volume expansion) L0 L V V + V

Lecture 24. Act 1 Thermal expansion As you heat a block of aluminum from o oc to 100 oC, its densit (a)increases(b)decreases (c)stays the same T=100C Solution T=OC Hereβ is positive Volume increases Density decreases M M, V1 Answer: (b) PO=M/VO P100=M/V 100 po Physics 121: Lecture 24, Pg 8

Physics 121: Lecture 24, Pg 8 Lecture 24, Act 1 Thermal expansion As you heat a block of aluminum from 0 oC to 100 oC, its density (a) increases (b) decreases (c) stays the same • Solution Here  is positive Volume increases Density decreases T = 0 C M, V0 r0 = M / V0 T = 100 C M, V100 r100 = M / V100 < r0 Answer: (b)

Lecture 24 Act 2 Thermal expansion An aluminum plate(a=24x10-b) has a circular hole cut in it. A copper ball (solid sphere, a=17x10-) has exactly the same diameter as the hole when both are at room temperature and hence can just barely be pushed through it. If both the plate and the ball are now heated up to a few hundred degrees Celsius how will the ball and the hole fit (a) ball won't fit (b) fits more easily (c)same as before Physics 121: Lecture 24, Pg 9

Physics 121: Lecture 24, Pg 9 Lecture 24, Act 2 Thermal expansion An aluminum plate (=2410-6 ) has a circular hole cut in it. A copper ball (solid sphere, =1710-6 ) has exactly the same diameter as the hole when both are at room temperature, and hence can just barely be pushed through it. If both the plate and the ball are now heated up to a few hundred degrees Celsius, how will the ball and the hole fit ? (a) ball won’t fit (b) fits more easily (c) same as before

Special system: Water Most liquids increase in volume with increasing T p(kg/mo) water is special density increases from 0 to 4oC ice is less dense than liquid water at4°C hence it floats water at the bottom of a pond is the denser, i. e. at 4 oC T(°C) Water has its maximum density at 4 degrees Reason: chemical bonds of H2o (see your chemistry courses Physics 121: Lecture 24, Pg 10

Physics 121: Lecture 24, Pg 10 Special system: Water Most liquids increase in volume with increasing T water is special density increases from 0 to 4 oC ! ice is less dense than liquid water at 4 oC: hence it floats water at the bottom of a pond is the denser, i.e. at 4 oC Water has its maximum density at 4 degrees. r(kg/m3 ) T (oC) Reason: chemical bonds of H20 (see your chemistry courses !)