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Chapter 8 - Transfer of Thermal Energy!

Thermal energy always flows from a region of higher temperature to a region of lower temperature!

Thermal engery can be transfered by these processes: Conduction, Convection & Radiaton! (aka CCR)

heres a picture to summarise what is CCR!



1) Conduction

Conduction is the process of thermal energy transfer without any flow of the material medium.

conduction race! :D


therefore, we can conclude 2 important points:
-Thermal energy flows through the materal of each rod without any flow of the material itself.
-Different material conduct heat at different rates. Copper is good conductor of heat while steel is a poor conductor of heat (aka insulator)

so, how does conduction work?
When a rod is heated at one end, the particles of the hot end will vibrate vigorously, colliding with neighbouring particles, making them vibrate as well. Therefore, kinetic energy of the vibrating particles at the hot end is transferred to the neighbouring particles.

JAVA SCRIPT --> (The one on the left is the conduction example) CLICK HERE! :D

note that the particles at the hot end vibrating vigorously while the particles at the cooler ends vibrating less vigorously (:

2) Convection
convection is the transfer of thermal energy by means of currents in a fluid (liquid/gas)

convection in liquid


convection in air

(actually i found one almost the same as the experiment to show convection in air, but the experiment doesnt seem to work, take a look if you want --> HERE! :l)

SOOO, how does convection work?
In water - when water is heated, it expands. Expanded water is less dense than the surrounding water, therefore it rises while the cooler water is denser, sinks.

In air - The heated air expands & becomes less dense, rises, while the surrounding air, being denser, sinks. JAVA SCRIPT ON CONVECTION IN AIR ---> CLICK HERE! :D (its the one on the right)

3) Radiation

radiation is the continual emission of infrared waves from the surface of all bodies, transmitted without the aid of a medium.

*note! unlike conduction & convection, it does not require any medium for energy transfer!

-Infrared radiation is absorbed by all objects & surface, this cause a temperation rise.

Factors affecting rate of infrared radiation:

1) Colour & texture of the surface
Black surface absorbs & emits infrared radiation better then shiny, white surfaces.

2)Surface temperature
The higher the temperature of the surface of the object relative to the surrounding temperation, the higher the rate of infrared radiation.

3) Surface area
The greater the surface area, it will emit infrared radiation at a higher rate.

To be continued with the applications of thermal energy transfer... (: