Thermal physics

Temperature

the number which determines whether 2 objects are in thermal contact are in thermal equilibrium or not

Heat

a flow of energy

Diathermic

insulating

Thermal contact

if heat is allowed to flow we say they are in thermal contact

Thermal equilibrium

2 systems are in equilibrium only if they have the same temperature

Thermal expansion

increase in temperature causes things to expand

Invar

specially designed to have a very low thermal expansion coefficient

Thermal stress

change in temperature but preventing it from expanding or contracting

Heat transfer

1. Conduction

2. Convection

3. Radiation

Conduction

Flow of heat directly through a physical material

Animals and thermodynamics

Polar bears have insulating hair. Seals and walrus's can keep warm because of a thick layer of blubber

Leiden frost

Rapid heating generates vapour layer, insulating layer created

Convection

The transfer of heat by the mass motion of fluid. Occurs when a fluid is unevenly heated

Radiation

the transfer of heat by electromagnetic waves such as visible light or infrared

Emissivity

a factor which depends on the nature of the surface.