TRANSFERING OF THERMAL ENERGY.

OBJECTS become hot when heat is supplied to it.
*Thermal energy flows from a region of higher temperature to a region of lower temperature. [just like winds (:]

The greater the difference between the hot and cold objects, the greater the heat flow.
Q: why do we flush the ice tray with water before we take the ice?
A: that's because the ice is stick to the ice tray and the heat from water will flow to the ice to make it melt a bit so that we could later take out the ice from the ice tray.

Differences between temperature and thermal energy:

Temperature is the measure of how hot an object is. SI unit: Kelvin.
Thermal energy is the flow of energy from a hot object to a cold object. SI unit: joule.

There are 3 mechanisms for thermal energy to flow, they are conduction/ convection/radiation.


CONDUCTION: heat transfer in a medium without the movement of the medium itself.
heat transfer through:
1.vibration of particles> heat is been passed by particles through vibration and because particles in solids are closely packed together, solids conduct heat better than liquids/gases.
2.motion of free electrons>electros in objects tansfer energy, and because metals have more free electrons(delocalised electrons), they condust heat better.


CONVECTION: heat transfer in a medium by the movement of particles in it, so it only take place in liquids and gases. (particles in solids are not able to move about.)
*convection current is brougth by hot fluid rises/ cold fluid sinks mechanisms.( the density of the particle changes but not the size.)

*Volume increases, density decreases. Volume decreases, density increases.
1. convection current in liquids>when liquid is heat, it's density decreases and hot fluid rises.cooler part of the liquid later then sink. (shown by coloured dye)
2. convection current in gases>when gases are heated up, they expands and become less dense. hot gases rise up and because the cooler part of the gas has higher density, so, the cooler part of the gas sinks down. (shown in sea/ land breeze... it's getting more and more like geography)

RADIATION: heat transfer by infrared waves.*doesn't need particles, therefore, it can take place in vacuum.
Radiator/Emitter>substance that gives away heat in the form of radiation.[it's temperature falls when radiates heat]
Absorber>substance that takes in heat in he form of radiation.[it's temperature rises as it receives heat]
Reflector>substance that bounce off radiation.
factors of rate of heat transfer by radiation:
1.color and texture of thesurface>Quality and color of the objects.
-Black/dull/rough surface are best absorber of heat/poor reflector of heat.
-white/shiny/smooth surface are poor absorber of heat/best reflector of heat.
2.surface temperature>higher the temperature of the surface, higher the rate of infrared radiation from it to the surroundings.
3.surfacr area>larger the area of the object, the greater the rate of infrared radiation from it to the surrounding.
( (That's why mii wei always like to wear all black, coz she wants to loose weight! And don't go any closer coz she's hot!)
Okay yup, this is about chapter 8. Haiz i need to blog about chapter 9 now. Awww... it's due by today and i didn't know until jolene/steph and yuxian tell me! btw thanks! muacks<3