Conduction, Convection, Radiation, oh my!!

Conduction

– Involves objects in direct contact– 2 objects in contact are at unequal

temperature– Example: a wire coat hanger with a

marshmallow on it over a fire

Convection

– Results from the movement of warm fluids; the movement of the heated substance itself

– Example: fig. 8 – air close to fire gets hot and expands so that there’s more space between the air particles, the air becomes less dense and moves upward, carrying extra energy with it, the rising warm air is replaced by cooler denser air

Convection– Convection current - the cycle of a heated

fluid (gas or liquid) that rises and then cools and falls• When a pan of water is heated, the water at

the bottom gradually rise and heat the molecules toward the top

• When a room is heated and cooled convection currents are used

Radiation

– Does not require physical contact between objects– Ex: as you stand before a campfire you feel its

warmth – your skin absorbs the energy radiated by the fire so the average kinetic energy of the molecules in your skin increases and thus the temperature in your skin

Radiation

– Is transferred in the form of electromagnetic waves and is called radiation

– Does not involve the movement of matter so radiation is the only form of energy transfer that can take place in a vacuum (outer space)

– Energy from the sun travels through space by radiation ONLY

Conductor

• Conductor – any material through which energy can be transferred as heat – Good – metals– Bad – gases (particles are far apart and

transfer of energy is less likely to occur); liquids (not as bad as gases, but not effective)

Insulator

• Insulator – any material through which energy cannot be transferred as heat– Good – rubber and wood