Introduction to Thermal Physics What is Temperature? •The degree of hotness or coldness of a body or environment. •A measure of the warmth or coldness of an object or substance with reference to some standard value. •A measure of the average kinetic energy of the particles in a sample of matter, expressed in terms of units or degrees designated on a standard scale. •A measure of the ability of a substance, or more generally of any physical system, to transfer heat energy to another physical system. •Any of various standardized numerical measures of this ability, such as the Kelvin, Fahrenheit, and Celsius scale. How a Thermometer Works As the temperature of the liquid in a thermometer increases, its volume increases. The increase in volume is thus due to a change in height of the liquid within the column.

Celsius  water freezes at 0 and boils at 100 degrees Temperature Scales Kelvin temperature scale, which is the standard metric system The zero point on the Kelvin scale is known as absolute zero. Celsius  water freezes at 0 and boils at 100 degrees Fahrenheit  water freezes at 32 and boils at 212 degrees Kelvin  zero is absolute zero (-273 degrees C)

What is Heat? Heat is simply the transfer of energy from a hot object to a colder object. Thermal Equilibrium

Methods of Heat Transfer Conduction – heat transferred between materials in direct contact Conductors – materials that transfer heat energy well - elements with loosest outer electrons are best - silver, copper best followed by aluminum then iron Insulators – materials which delay the transfer of heat energy - compounds with trapped air spaces - liquids and gases Convection – heating that occurs through currents in a liquid or a gas used to heat and cool homes and buildings provides the engine which produces wind Radiation – heat transmitted through electromagnetic waves radio waves, microwaves, infrared, visible light, ultraviolet, x-rays, gamma rays longest shortest wavelengths Lower temperatures emit longer waves Higher temperatures emit shorter waves

Transmission of Heat Radiant Energy – any energy transmitted by electromagnetic waves (radiation)  As an object gets hotter, some of its radiant energy is given off as visible light Absorption – opposite of reflection  good absorbers reflect very little radiant energy  good reflectors are poor absorbers  good absorbers are good emitters

The Greenhouse Effect Terrestrial Radiation – long wave radiation emitted by earth into outer space Solar Radiation – short wave radiation emitted by the sun The greenhouse effect is a result of the atmosphere’s inability to release our terrestrial radiation