Thermal Energy! An Intro. to Heat and Temperature CH21 Physics (B) Winter,

Objectives  Temperature & Its Scales  Heat  Thermal Equilibrium  Internal Energy  Measurement of Heat  Specific Heat  Play With Fire!!!! (Safely ) 2

What is Temperature T?  Temperature (Symbol is T) measures the “hotness” of an object – The hotter it is, the higher T – The colder it is, the lower T – Must have a standard temperature to compare, a CONTROL  Measured many types of sensors: (Infrared Temp Sensor, Thermocouple, Thermometer)  T IS NEVER EVER NEVER HEAT!!!!! 3

What’s the Scale to Measure Temp?  There are THREE scales! 1.(°F) 2.(°C) 3.(K, just K)  When do we use what? 1.In Physics class, always (°C) 2.In Nursing and Weather in USA, (°F) 3.In Astronomy, (K) most of the time 4

Typical Values of Scales  Fahrenheit Scale: – H 2 O Boiling Pt: 212 std. pressure – H 2 O Freezing Pt: 32 std. pressure – Human Body = 98.6 (°F) 98.1 (°F) for Harvard!  Celsius Scale: – H 2 O Boiling Pt: 100 std. pressure – H 2 O Freezing Pt: 0 std. pressure – Human Body = 37 (°C)  Kelvin Scale: – Sun is ~ 5700 (K) – Stars range from 2000–26,000 (K) (hot!) – Absolute Zero: 0 (K) lowest possible temp. 5

Do You Want to Convert Between the Two?  °F = (°C x 1.8) +32(Eq. 1) – Use this to go FROM Celsius TO Fahrenheit  K = °C (Eq. 2) – Use this to go FROM Celsius TO Kelvin  Put these on your formula sheet 6

Specific Heat, c  Specific Heat = the resistance of change to a body’s temperature (a material property)  Symbol = Little c (Big C is already Celsius!)  Metric Units: ( J ) ( kg°C )  Specific Heat = THERMAL INERTIA  The higher the Specific Heat, the more resistant to change temperature  H 2 O is HIGHEST: 4186 ( J ) kg°C  Copper wire is low: 386 ( J ) kg°C  Human body is High: 3470 ( J ) kg°C 7

What Makes Something HOT?  Old Theory (1700s): – Caloric Theory-we believed an invisible fluid (caloric) was added to a body when heated….needed a heat source – Didn’t hold up in all cases: hands rubbed together got warm (no external heat source)  New Theory (1850s): – Kinetic-Molecular Theory: All bodies are made up of tiny particles that are always in motion – Hot bodies: particles move faster with higher energy than cold bodies – Temp. measures the AVERAGE kinetic energy of these moving particles 8

Then, What is Heat?  Heat is the thermal energy that flows as a result of a difference in temperature (ΔT)  Heat Temperature Total KE  Symbol (letter NOT in parentheses): Q  Units (the stuff in parentheses): J – joules, J in Metric System (Nm) – The stuff in parentheses  Heat (energy) always travels from Hot to Cold  Eventually, the hot body moves so much heat energy to the cold body, they become one temperature at thermal equilibrium  Thermal Equilibrium is ΔT=0, or T final = T initial or T hot = T cold 9

What is Thermal Energy?  Well, there’s KE & PE from Physics (A)  Thermal Energy = Internal Energy, UE  Thermal Energy = sum of object’s internal motion (all these particles moving to make energy)  KE + PE = UE (Eq. 3)  For this class, Internal Energy = Thermal Energy, UE 10

Let’s Go Play With Fire! (Safely ) 11