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.

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)

Heat is simply the transfer of energy from a hot object to a colder object.

What is Heat?

Thermal Equilibrium

Methods of Heat TransferConduction – heat transferred between materials in direct contactConductors – 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