FUNphysics;

2008-09-06T16:45:00.000+08:00

went around youtube searching for some physics videos, but found this!

SUPERCOOOOOLING! :D omgggg, i think its so cooooooooooooooooool. hahas,

''Supercooling is the process of chilling a liquid below its freezing point, without it becoming solid.'' - Wikipedia

2008-09-04T00:30:00.000+08:00

Chapter 9 - Thermal Properties of Matter

What is internal energy? o.O
- Internal energy is particles in a solid vibrating about in a fixed position & are held together by strong interatomic/intermolecular bonds.
-Internal energy comprises of 2 components - kinetic energy & potential energy

Kinetic Energy
- Is the vibration of the particles
- Directly related to temperature
- The higher the temperature, the more vigorous the vibration of the particles
- For liquid & gas, kinetic energy is due to their movement
- One example is the mircowave oven :Dthats why your ice cold food get pipping hot in few seconds! :D

Potential Energy
- Is the stretching & compressing of intermolecular bonds as the particle vibrates
- Amt of potential energy stored in the bonds depends on the force between the particles & how far apart they are.
- One example is the slinky :D

Melting
- Is when a solid changes to a liquid upon heating.
must appreciate this graph, okay! cause i took a million years to draw! :D but any mistakes, pls do correct me :/

one example is ice melting -

So how does a soild melt?
Molecules in a soild are held by strong intermolecular bonds. Thermal energy is supplied to the soild, breaking the intermolecular bonds, allowing the molecules to move out of their fixed positions.

Solidification & Freezing point
- The reverse process of melting ( changing from a liquid to solid )
- Freezing point is the point whereby the liquid freezes to becomes a solid - -Condensation
- Is the change of state from vapour to liquid when it is cooled at the same temperature as boiling.
- Thermal energy is given out
one example is the morning dew! :D
Boiling
- When a liquid is heated & changes to a gas at a fix temperature is called boiling. & that particular temperature is called its boiling point
- Reverse of boiling is condensation

Evaporation
- Evaporation can occur at any temperature

Apllications of evaporation
1) Cooling effect when any liquid evaporates from your skin
2) A puddle of water dries up after some time
3) Whenever you're sick, your mama will put a wet cloth on your forehead & when the water evaporate, there will be a cooling effect, keeping temperature down.

Factors affecting the rate of evaporation

1) Temperature
The higher the surrounding temperature, the higher the rate of evaporation.

2) Humidity of the surrounding air
Rate of evaporation increases with decreasing humidity.

3) Surface area of liquid
More surface area exposed to the air, rate of evaporation will increase.

4) Movement of air
Moving air increases the rate of evaporation.

5) Pressure
Reducing the atmospheric pressure increases the rate of evaporation

6) Boiling point of the liquid
Liquids with lower boiling points will evaporate faster.

2008-09-03T01:40:00.000+08:00

Chapter 8.5 - Applications of Thermal Energy Transfer

Uses of good conductors of heat

1) Cooking Utensils
Imagine, your cooking pot is made out of wood/plastic, its gonna take a billion years for your food to get cooked. That is why our cooking pots, saucepans are made out of metal, this is to ensure direct heating is involved.

2) Soldering iron rods
the tip is made out of copper as copper is a better conductor of heat then iron.

3) Heat exchangers
helps save energy, mostly used in large laundry facility.

Uses of bad conductors of heat (aka insulators)
1) Handles of appliances & utensils
do you notice that your cooking pots, saucepans, kettles have handles that are made out of plastic? this is because plastic are insulators & it will prevent us from burning our hands! :D

2) Table mats
they are made out of cork so that your super hot kitchenware can be placed on the table mats without damaging your beautiful table.

3) wooden ladles
extremely useful for stirring your soup or scooping up rice.

Common applications of convection

i remember we learnt something from geography about convection!

1) Convection currents in the mantle

remember to click to enlarge! & paiseh, i scan until like that. hhahas

&&&&&

2) Sea & Land Breezes
YAY! physics & geography can relate! :D :D :D

3) Radiator

Common applications of radiation

1) Teapot
have you ever wondered why is your teapot always made out of shiny material & not dark materials? remember the 3 factors of the rate of infrared radiation? As shiny surfaces are bad absorbers of radiation, it can keep your drinks hot longer then dark surfaces (:

2) Greenhouse
infrared radiation passes through the glass roof of the greenhouse & this warms up the plants & soil. When these plants & soil gets warm, they emits infrared radiation too. however, this infrared radiation is unable to pass through the glass roof as it is different from the sun's infrared radiation. the amt of infrared radiation will slowly build up, causing the temperature to rise in the greenhouse.

3) Vacuum flasks
made to minimise heat loss in 4 ways, conduction, convection, radiation & evaporation.Stopper - is usually made out of poor conductors of heat.
Vacuum - conduction & convection is prevented by the vacuum
Silvered surface - to minimise heat loss thru radiation & it is able to reflect the radiant heat heat to the liquid, keeping the liquid warm.

2008-09-02T16:40:00.000+08:00

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... (:

2008-09-01T14:45:00.003+08:00

Chapter 7 - Kinetic Model or Matter

Solid

Properties:
-Fixed shape & volume
-Hard & Rigid
-High Density
-Incompressible

-Particles are closely packed in a regular pattern, occupying minimum space resulting in solids having high densities.
-Particles also vibrate about fixed positions as they are held in position by very strong intermolecular bonds. This is why solids have a fixed volume and shape.

Liquid

Properties:
-Fixed volume but does not have a fixed shape
-High density
-Incompressible

-Particles of liquid are randomly arranged with particles slightly further apart then solids, therefore, this results in liquid having relatively high densities.
-The particles are free to move about but is confined within the vessel containing it & have attractive forces between the particles. Therefore liquids have fixed volumes but no fixed shape.

Gas

Properties:
-No fixed shape & volume
-Low density
-Compressible

-Particles are very far apart & are randomly arranged, occupying any available space, therefore, gases have very low density
-The particles of gas have very little attraction between them & move about randomly at very high speed. This explains why gases have no fixed volume, shape and is compressible.

Brownian motion
-is the random/irregular motion of smoke particles in air
-only occurs in fluids (any substance that is able to flow/has particles that can move freely)
-Higher the temperature, the motion of smoke particles will be come more vigorous. Therefore, we can conclude that air molecules have greater speed at higher temperatures.

java applet -->Brownian Motion

2008-08-27T17:50:00.002+08:00

YAY! BLOG DONE! :D

thermalphysics;thermalphysics :l