Temperature vs. Heat vs. Internal Energy Work in groups in 2-4 Collect a whiteboard and pens Make a Venn Diagram showing how the terms Temperature, Heat and Internal Energy are similar and different Use your notes and phones for resources!

Thermal Physics AP Physics B

Thermal Physics B. Temperature and heat 2% Mechanical equivalent of heat Zeroth Law of Thermodynamics Latent Heat Heat transfer and thermal expansion Conduction Convection Radiation C. Kinetic theory and thermodynamics 7% Ideal gases Kinetic model Ideal gas law Laws of thermodynamics First law (including processes on pV diagrams) Second law (including heat engines)

Temperature and Heat Temperature: physical property of matter that quantitatively expresses the common notions of hot and cold. The temperature varies with the microscopic speed of the fundamental particles that it contains (or their kinetic energy).

All particles have internal movement... ALWAYS Temperature measures the average Kinetic Energy of the particles within a substance NOT the total energy of the substance, which depends on it’s mass

Basis for Temp Scales Fahrenheit: Oldest scale, Freezing point is 32oF, Boiling point 212oF ~ makes no sense… Celsius: Water Freezes/Melts at 0oC, and boils at 100oC Kelvin: 0oK is the coolest theoretical temperature possible, no negative Kelvins. Same increments at Celsius Scale. Basically an updated version of the Celsius scale

Temperature Scales:

Absolute Zero – 0 Kelvin Q: What would have to happen in order to reach absolute zero? Atoms and subatomic particles would have to stop moving… impossible. 2003 - MIT scientists cooled sodium gas to the lowest temperature ever recorded -- only half-a-billionth of a degree above absolute zero.

Zeroth Law of Thermodynamics If Tx = Ty and Ty = Tz, then Tx = Tz Well … Duh! Why Zeroth Law???? Made after Laws 1,2, and 3

Heat Heat: Transmission of energy from one body to another due to temperature difference (hot to cold) – unit is Calorie or Joule We will talk about Heat Transfer when we discuss the Mechanical Equivalent of Heat

Internal Energy Compare TOTAL INTERNAL ENERGY of gas to liquid/solid Study liquids/solids now…ideal gases later

Heat Take Home Message(s) Heat is a process Matter contains internal energy NOT HEAT Heat is the transfer or conversion of energy Compare to Work and Mechanical Energy…

In-Class Work + Homework Collect the worksheet from the front of the room Please watch the Video – 2 for homework! + MC Q’s: 6, 24, 30, 32, 35, 39, 58 ALSO: Watch Specific Heat Video if you haven’t already done so!

What’s next? How? – Next Class! Quiz! + … Conduction: molecular collisions Convection: motion of fluid Radiation: no medium necessary (EM waves)

AP Phys 12 – Class Starter Quiz: Temperature and Heat Transfer! Please clear everything off your desk except a pencil and calculator Collect Data Sheets and a scrap piece of paper from the front of the room Wait for the quiz! When finished collect a new Quiz Log from the front!

Whiteboarding! Please work in groups of 2 Collect a Whiteboard and Pens Let’s review a few concepts!

Heat, Thermal Energy and Internal Energy: Words of caution! “To describe the energy that a high temperature object has, it is not a correct use of the word heat to say that the object "possesses heat" - it is better to say that it possesses internal energy as a result of its molecular motion. The word heat is better reserved to describe the process of transfer of energy from a high temperature object to a lower temperature one. You can take an object at low internal energy and raise it to higher internal energy by heating it. But you can also increase its internal energy by doing work on it, and since the internal energy of a high temperature object resides in random motion of the molecules, you can't tell which mechanism was used to give it that energy.”

Heat Transfer Due to ΔT All materials are not created equally in terms of heat transfer Would you rather touch your tongue to a 0 C metal pole or wooden pole? Why?

Thermal Conductivity, k k is a measure of an object’s ability to conduct heat (transfer) Higher k means faster rate of transfer Materials of high thermal conductivity are widely used in heat sink applications and materials of low thermal conductivity are used as thermal insulation H – Rate of Heat Transfer (J/s or kcal/s) A – Area L – thickness

Question: Find H of the glass below in J/s

Table 14-4 Thermal Conductivities

Question: Find H of the glass below in J/s Ans: 7.9 x 102 J/s

Question What is a better insulator, an object with a larger k, or smaller k?

Question What is a better insulator, an object with a larger k, or smaller k? Ans: Smaller k!

Question If air has such a low thermal conductivity (0.22), why do we need to wear clothes? (Other than for decency reasons…)

Question If air has such a low thermal conductivity (0.22), why do we need to wear clothes? (Other than for decency reasons…) ANS: Air is always moving, we use clothes to trap air close to our bodies. The thicker the clothes the more air we trap.

Specific Heat: Heat Transfer with Changes in Temperature Q = mc∆T Heat transfer depends on amount of material (m), temperature difference (∆T), and material property (c) c = specific heat – amount of heat/mass required to raise temperature by 1 degree Note: Specific Heat was covered in Physics 11

Water vs. Copper Which has a greater internal energy? cwater = 1 cal/g oC = 4186 J / kg oC ccopper = 0.093 cal/g oC = 389 J / kg oC 1 gram of copper at 0 oC and 1 gram of water at 0 oC If heated by 1oC…. Which has a greater internal energy? Same kinetic energy (temperature is the same) Water has more internal energy due to higher specific heat (requires more heat to increase kinetic energy of particles)

Specific Heat: Heat Transfer with Changes in Temp ΔQ = 0 (closed system) Q heat IN = Q heat OUT Same Q transfers, different objects (ignore -/+!) Big mass vs. small mass: small mass will get hotter Metal (lower c) vs. Wood (higher c): metal gets hotter ∆T= Q/mc

Hot Object Added to Cool Liquid -Qhot = Qcold mhotchot(Thot-Tfinal) = mcoldccold(Tfinal-Tcold)

Question 500. grams of 20.0o C water is added to 700. g of 85o C water. What is temperature of the mixture?

ANSWER 500. grams of 20.0o C water is added to 700. g of 85o C water. What is temperature of the mixture?

Question We wish to determine the specific heat of a new alloy. A 0.150 kg sample of the alloy is heated too 540o C. It is then quickly placed in 400. g of water at 10.0o , which is contained in a 200. g aluminum calorimeter cup. (Assume that the insulating jacket insulates well, so the temperature does not change significantly). The final temperature of the mixture is 30.5o C. Calculate the specific heat of the alloy. cw = 4186 J/kg oC ; ccal = 900.0 J/kg oC -mscsΔT = mwcwΔT + mcalccalΔT Remember, Heat LOST = Heat GAINED (this changes your ΔT)

ANSWER – 497 J/kg oC cw = 4186 J/kg oC ; ccal = 900.0 J/kg oC We wish to determine the specific heat of a new alloy. A 0.150 kg sample of the alloy is heated too 540o C. It is then quickly placed in 400. g of water at 10.0o , which is contained in a 200. g aluminum calorimeter cup. (Assume that the insulating jacket insulates well, so the temperature does not change significantly). The final temperature of the mixture is 30.5o C. Calculate the specific heat of the alloy. cw = 4186 J/kg oC ; ccal = 900.0 J/kg oC Remember, Heat LOST = Heat GAINED (this changes your ΔT) Heat lost Heat gained

Phases and Phase Changes

Question: Why doesn’t the temp increase at 0o C and 100o C?

Energy Input goes to enabling the Phase Change

Heat Transfer w/out Changes in T (Phase Changes) If No ∆T: Phase change MUST be occurring Input of energy is used to break intermolecular bonds Q = m x L Heat transfer depends on how much (mass), and material property (L) L = latent heat of fusion (melting/solidifying) or vaporization (vaporizing/condensing) Lf water = 3.33x105 J/kg Lv water =2.26x106 J/kg

Total Heat Go from -50 C to 120 C… Qtotal = Q-50-0 + Q0 + Q0-100 + Q100 + Q100-120 Qtotal = mc(50) + mLf +mc(100) + mLv + mc(20) Qtotal = mc(170) + mLf + mLv

Question How much energy does a refrigerator have to remove from 1.5 kg of water at 20.0o C to make ice at -12o C. The Heat of Fusion is 3.33 x105 J/Kg, the specific heat of water is 4180 J/(kgoC), the specific heat of ice is 2100 J/(kgoC).

ANSWER How much energy (in kJ) does a refrigerator have to remove from 1.5 kg of water at 20.0o C to make ice at -12o C. The Heat of Fusion is 3.33 x105 J/Kg, the specific heat of water is 4180 J/(kgoC), the specific heat of ice is 2100 J/(kgoC).

Joule’s Experiment - GENIUS

Video – Mechanical Equivalent of Heat

For the Rest of Class! Complete the Heat Transfer Worksheet Heat Transfer – AP Questions: MC: 10, 26, 28, 42, 43, 53, 56, 65, 81

Now what… Next Video: Ideal Gases MC Question’s: 2, 5, 7, 9, 21 -23, 27, 31, 38, 44, 45, 47, 48, 51, 52, 61-64, 73, 76, 78 Next Class: Quiz on Ideal Gases + Gas Law Simulation (Please bring a computer!)