EK

2008-09-05T14:00:00.003+08:00

Heeee(:
was trying to find some funny things to post to mark the end of finishing the race of Physics Blog, BUT....

Hahaha, but ended up looking at Garfield's jokes. LOL.
Found this rather hilarious one. (:

Get the joke?
it is okay if you dont . (:

2008-09-03T12:04:00.011+08:00

CHAPTER 9;
Thermal Properties of Matter.

The unit for Thermal energy is joule (J).

The intermolecular bonds that binds particles together, is called Internal Energy.

Internal Energy consists of two components - Kinetic & Potential Energy.

Vibration of particles results in Internal Kinetic Energy.

Stretching & Compressing of the intermolecular bonds by vibration of particles, results in Internal Potential Energy.
The higher gain of Thermal Energy in heating, the higher the temp. will be.

Amount of Potential Energy stored in bonds depends on the force and distance between particles.

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PICTURES!

[Pic.1 Microwave] This reflects of Point number 4.

[Pic.2 Slinky] This reflects of Point number 5.
[Pic.3 Process of heating water] This reflects of Point number 6.-------------------------------------------------------------------------------------------
This is to summarise all processes:
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Melting & Solidification:

Melting is the process of solid changing into liquid state. E.g: Ice melts to become water.

The melting point of ice is at 0 (Degree Celsius).
The change of state doesn't affect its temperature.

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Solidification (Freezing point) is the process of liquid changing into solid state. E.g: By putting water in freezer, the water is being freezed into ice.

This diagram shows the process of Solidification:

Mainly, from a state of liquid, go into process of Solidification, and reach to state of solid.
============================================================
Boiling & Condensation:

Boiling is the process of liquid changing into gaseous state (vapour).

From ice, goes through a process of freezing point. Upon turning into a liquid, as temperature increases,
goes through a process of boiling.
And finally become vapour in a gaseous state.

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Condensation is a process of gas changing into a liquid state.
Thermal Energy is being givent out during Condensation.

A glass of COLD WATER, comes in contact with the surrounding WARM MOIST AIR,
goes through the process of Condensation,
and transform into tiny water droplets (liquid).

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Evaporation:

Evaporation is the process of liquid changing into gaseous state. (like Boiling)
Evaporation is able to take place at any temperature.

However, the process is much slower than Boiling.

With heat, the water evaporates faster than without heat.
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Applications of Evaporation:

Cooling effect will occur when perspiration evaporates.

Puddles of water on surface, will evaporate upon a period of time.

A high fever patient that is sponged with water, through Evaporation, is able to bring the patient's temperature down.

Refridgerator uses processes of Condensation & Evaporation, to keep food cool.

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Factors affecting the rate of Evaporation:

Temperature: The rate of Evaporation increases as the temperature increases.

Humidity of the surrounding air: The rate of Evaporation will decrease with increasing Humidity.

Surface area of the liquid: The rate of Evaporation increases as the surface area is more exposed.

Movement of air: The rate of Evaporation increases when the surrounding air is moving.

Pressure: The rate of Evaporation increases as the atmospheric pressure decreases.

Boiling point of the liquid: The rate of Evaporation increases when boiling point decreases.

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Video of Condensation process:

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This marks the end of Chapter 9; Thermal Properties of Matter :D
(Officially started at 10:07AM and ended at 12:04PM)

2008-09-02T23:09:00.004+08:00

CHAPTER 8;
Transfer of Thermal Energy.

Thermal energy is the energy portion of a system that increases with its temperature.
It is also a term used to describe the energy content of a system related to heating effects.

It can only be transferred when temperatures are in difference.

& in conclusion, Thermal Energy flows from a region of HIGHER temperature to a region of LOWER temperature.

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Thermal Energy is being transferred by 3 processes:

CONDUCTION.
CONVECTION.
RADIATION.

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Conduction:
It is the process of thermal energy being transferred without any flow of material medium.

An example of HEAT TRANSFER OF CONDUCTION:
Conduction occurs through collisions between atoms and molecules in the substance and the subsequent transfer of kinetic energy.

Study the following diagram:

When the barrier is removed, the fast ('hot') atoms collide with the slow ('cold') ones.

In such collisions, the faster atoms lose some speed & the slower ones gain speed; thus, the fast ones transfer some of their kinetic energy to the slow ones.

This transfer of kinetic energy from the hot to the cold side is called a flow of heat through CONDUCTION.

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An example of THERMAL CONDUCTIVITY:
Different materials transfer heat by conduction at different rates;

Study the following diagram:

Thus,

Materials with a HIGH thermal conductivities, will transfer large amounts of heat over time - e.g: Copper, that are good thermal conductors.

Similarly, materials with LOW thermal conductivities, will transfer small amounts of heat over time - e.g: Concrete, that are poor thermal conductors.

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Poor thermal conductor keeps as much heat in, as possible. Insulation is therefore also known in terms of its thermal resistance.

& in conclusion,

Materials that have a HIGH thermal conductivity, have a LOW thermal resistance -
Similarly, materials that have a LOW thermal conductivity, have a HIGH thermal resistance -
=========================================================================
Convection:
It is a process of thermal energy being transferred by means of currents in liquid or gases.

An example of HEAT BY CONVECTION:

As air heats, the molecules spread out; causing this region to become less dense than the unheated air.

Being less dense than the unheated air, the hot air will subsequently rise due to buoyant forces.

This movement of hot air into a cooler region is then said to transfer heat by convection.

Study the following diagram:

(arrows in the diagram are the CONVECTION CURRENTS)

Heating a pot of water on a stove is an example of transfer heat by convection.

When the stove is first turned on, heat is being transferred first, by conduction between the element through the bottom of the pot to the water.

However, when the water starts bubbling - these bubbles are actually regions of hot water rising to the surface, thereby transferring heat from the hot water, that is at the bottom; to the cooler water at the top, by CONVECTION.

At the same time, the cooler & denser water at the top, will sink to the bottom, where it is subsequently heated.

This is the process of CONVECTION, by heat transfer to form convection currents.

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An example: Flow of material through pressure difference

Study the following diagram:

When the barrier is being removed, material in the high pressure (high density) area will flow to the low pressure (low density) area.

This movement of material is said to be of heat flow by convection.

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Radiation:
It is a process of continual emission of infrared waves from the surface of all bodies, that transmit without a medium. (it can take place in vacuum.)

The energy of heat can go in making light, such as coming from a hot campfire.

This light, being a wave, carries energy. It can move from one place to another without requiring a medium.

When this light reaches us, part of the energy gets converted back into heat, which is why we are able to feel warm sitting beside a campfire.

Some of the light can be in the form of visible light, but a great deal of the light emitted, is infrared light.

The hotter the object is, the less infrared light is emitted, and the more visible light as well.

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Factors that affects the rate of infrared radiation:

Colour & texture of surface. Black surfaces are much better absorbers & emitters of infrared radiation, than white or shiny surfaces.

Surface temperature. The HIGHER the temperature of the surface of the object, the HIGHER the rate of infrared radiation.

Surface area. The LARGER the surface area is, the HIGHER the rate of emitting infrared radiation.

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Application of Thermal Energy Transfer (conduction):

Metals that are good conductors of heat are:

Cooking Utensils. e.g: Kettles, saucepans & boilers.
Soldering iron rods. (made out of Copper)

Heat exchangers. (made out of Copper too)

Non metals that are good insulators of heat are:

Handles of appliances & utensils. e.g: (handles of the above stated no.1 & no.2 )

Table mats. (made out of cork)

Sawdust.

Wooden ladles.

Woollen clothes.

Fibreglass, felt & expanded polystyrene foam.

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Application of Thermal Energy Transfer (convection):

Electric Kettles.

Household hot water systems.

Air conditioners.

Refrigerators.

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Application of Thermal Energy Transfer (radiation):

Teapots.

The Greenhouse. (used to help plants grow better by trapping heat)

Vacuum Flasks. (to keep liquids hot by minimising heat loss in CONDUCTION, CONVECTION, RADIATION & EVAPORATION)

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VIDEOS!

Thermal Conduction:

Thermal Convection:

With this, marks the end of Chapter 8, Transfer of Thermal Energy. :D
(officially started at 5:04pm and ended at 7:49pm) 1st half.
(officially continued at 10:06pm and ended at 11:09PM) 2nd half.

2008-09-02T16:41:00.009+08:00

CHAPTER 7 ;
KINETIC MODEL OF MATTER.

Matter is what makes up all substances.

It is the molecules and atoms that make up chemical substances.

Protons and electrons are examples of matter.

& in conclusion, Matter is anything that has mass and occupies space.

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Properties of Solids, Liquids & Gases:

SOLIDS

Fixed shape and volume.

High in density.
Incompressible.

LIQUIDS

Fixed volume.

NO fixed shape.
High in density.

Incompressible.

GASES

NO fixed shape & volume.
Low in density.
Compressible.

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Kinetic model of matter:

SOLID STATE:

Closely packed; thus, high in density.

Vibrate about their fixed positions that are held by strong intermolecular bonds; thus, fixed shapes & volumes.

LIQUID STATE:

Randomly arranged; thus high in density.

Move freely but within vessels that have forces between particles; thus, fixed volumes but NO fixed shapes.

GASEOUS STATE:

Far apart from each other. randomly arranged & occupies any space; thus, low in density.

Very little force between particles & moves randomly at high speed; thus, NO fixed shapes & volumes and resulting in having high compression.

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Brownian motion
It is a random movement of particles suspended in a liquid or gas.

When room temperature increases, these particles move faster and more vigorously in movement.
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VIDEOS!
SOLID, LIQUID, GAS.

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This marks the end of Chapter 7 ;
KINETIC MODEL OF MATTER.(:
(officially started at 2:43PM and ended at 4:41PM)

2008-08-27T21:27:00.003+08:00

Hello! :D
LETS ALL LOVE PHYSICS TOGETHER! *wooohoooo!*
LOL.
Btw, feel free to drop any comments :D