Temperature and Heat   Temperature and Thermometers   Is it hot or cold?   Mercury vs. alcohol Expansion or contraction of a material   Electrical resistance and infrared radiation 12/3/2015APHY1011

Temperature and Heat   Temperature scales   Reference points for setting the scale Why use water?   Triple point of water Solid, liquid and vapor all exist at the same time 12/3/2015APHY1012

Temperature and Heat   Absolute zero   Lowest temperature theoretically possible Lowest achieved is ~ 1x10 -9 K Average in space ~ 3 K   The KE is removed but not the quantum energy inside the atom – the electrons don’t stop moving   Is there a maximum temperature? 12/3/2015APHY1013

Temperature and Heat   Heat   Transfer of thermal energy between objects of different temperatures. Symbol: QUnit: joules ( J )   High temperature does not always mean high thermal energy   Other units: BTU, calorie, Calorie (food) 12/3/2015APHY1014

Temperature and Heat   Internal energy   Sum of KE (linear, rotational, vibrational) and PE (chemical bonds within and between molecules) Model   The thermal energy of the system 12/3/2015APHY1015

Temperature and Heat   Thermal expansion   Most substances expand as their temperature increases and contract when cooled   Each material has a different expansion rate   Examples: Pyrex glass, dental fillings, bridges, concrete 12/3/2015APHY1016

Temperature and Heat   Thermal expansion of water   Water expands as it cools from 4°C to 0°C Effect on ponds, lakes and roads during winter 12/3/2015APHY1017

Temperature and Heat   Specific heat   A constant that relates heat per unit mass and temperature change in a material Metals have low values and water has a high value   Thermal inertia Climate: land vs. oceans Pizza: crust vs. sauce 12/3/2015APHY1018

Temperature and Heat   Conduction   Energy transfer due to particle contact Atoms, molecules and electrons (metals)   Insulators and conductors Building materials Layers of clothing 12/3/2015APHY1019

Temperature and Heat   Convection   Energy transfer due to the motion of a fluid Currents are formed   Hot fluids rise and cold fluids sink Cooling occurs when a fluid expands Weather and climate 12/3/2015APHY10110

Temperature and Heat   Radiation   Energy carried by electromagnetic waves They can travel through empty space (vacuum) 12/3/2015APHY10111

Temperature and Heat   Radiation 12/3/2015APHY10112 UV IR Radio

Temperature and Heat   Radiation   All objects are emitters and absorbers of radiation   The rate of emission/absorption depends on the difference in T of the objects   Global warming The greenhouse effect 12/3/2015APHY10113