PHYS157 - 1d Heat flow: Conduction and Convection

why does heat flow from hot to cold?

The molecules in the warmer object vibrate faster than the ones in the cooler object. The faster vibrating molecules collide with the slower molecules

Explain why some objects feel colder than others even though they are the same temperature

• if better conductor = feel colder (draw heat energy from hand faster)

• your body loses heat faster (heat transfer=better because better conductor)

what is specific heat of an object

the quantity of heat required to raise the temperature of one gram of a substance by one degree celsius

(eg. c water = 4186)

relationship between conductivity and specific heat?

• conductivity=inversely proportional to specific heat

• low specific heat = higher conductivity

• high specific heat = lower conductivity.

what is thermal conductivity?

the ability of a material to conduct heat from its one side to the other

• smaller = stronger heat preservation/INSULATION

convection vs conduction

conduction = heat transfer occurs between objects by direct contact

convection = heat transfer within a fluid

Explain why heat current must be the same in all parts of a system where the temperatures/phases of various parts are not changing (flat parts of the graph)

• energy involved in a phase changes is used to break bonds

• no increase in the kinetic energies of the particles, and therefore no rise in temperature.

• energy is needed to vaporize a liquid to overcome the attractive forces between particles in the liquid