clarice's

2008-09-04T09:13:00.000-07:00

please kindly

click

on the archives of

september 2008

to view

all

the posts

from

chapter 7 to 9.

THANKS! :)

2008-09-04T09:06:00.000-07:00

FINISHED!

after two days of hard work, i have completed this entire blog
thanks to all those who have left their comments and who have viewed my blog.
and of course, thanks to those who have been asking me to ADD OIL

i never knew that bloggin can actually be so educational but yet so tiring
but i enjoyed blogging and learning at the same time

to all readers: thanks for viewing. hope that you learn something after viewing.

special thanks to : http://sg.images.search.yahoo.com/
for the pictures.

special thanks to the physics textbook which provided me with the informations :)

2008-09-04T09:02:00.000-07:00

EVAPORATION:

- shows water being evaporated.

-drying of hair

drying of wet clothes

puddles of water

puddles of water

2008-09-04T08:47:00.000-07:00

++ FACTORS AFFECTING THE RATE OF EVAPORATION.

1. temperature
>> higher the temperature of the liquid,
faster the rate of evaporation

!! heating a liquid will increase the rate of evaporation

2. humidity of the surrounding air
>> rate of evaporation decreases,
with increasing humidity

!! rate of evaporation increases with lower humidity

3. surface area of the liquid
>> rate of evaporation increases,
when there is more exposed surface area of the liquid

!! larger exposed surface area means more molecules can escape from the liquid

4. movement of air
>> rate os evaporation increases,
when the surrounding air is moving

5. pressure
>> reducing the atmosphere pressure,
increases the rate of evaporation.

6. boiling point of the liquid
>> liquids with lower boiling points will evaporate faster.

2008-09-04T08:42:00.000-07:00

how does evaporation occur?

~ molecules of liquid are always moving randomly at different speed
~ thermal energy may be absorbed by the liquid from the surroundings
~ at the liquid suface
>> molecules are more energetic
>> are able to overcome the downard attractive forces of other molecules
>> they escapes into the atmosphere

2008-09-04T08:38:00.000-07:00

appilcations of evaporation:

cooling effect on skin when applying perfume or when perspiration evaporates
wet clothes and puddles on water on pavements dry up after a while
sponging a patient with a high fever
refrigerators uses priciple of condensation and evaporation in cooling process to keep its contents cold

2008-09-04T08:28:00.000-07:00

+ EVAPORATION

~ like boiling, evaporation is the change of state from liquid to gas

~ evaporation can take place at any temperature.

©clarice2008

2008-09-04T08:05:00.000-07:00

+ Boiling and condensation

~ boiling:

- pure liquid is heated and changes state to vapour at fixed / constant temperature

- reverse of condensation

~ condensation

- chnge of state from vapour to liquid

- when substance is cooled at the smae constant temperature as in boiling

- thermal energy given out during condensation

how does a liquid boil?

>> thermal energy separate the molecules

>> molecules are futher apart with negligible intermolecular forces of attraction between them.

{ condensation }

{ boiling }

2008-09-04T08:01:00.000-07:00

++ lifting ice with string.

TRY IT OUT AT HOME ON YOUR OWN.

ITS PRETTY EASY!

2008-09-04T07:54:00.000-07:00

+ solidification and freezing point

- reverse process of melting : SOLIDIFICATION

- its the changing from a liquid to solid

!! where does the thermal energy go to since there is no change in temperature?

- when liquid molecules cometogether and solidify,

- intermolecular bonds are formed.

- as intermolecular bonds are formed,

- thermal energy is released

2008-09-04T07:45:00.000-07:00

+ Melting and Solidification

~ melting:

- when solid changes to a liquid upon heating.

how does a solid melts?

for solid to melt, bonds have to be broken
thermal energy helps in the breaking of intermolecular bonds
when intermolecular bonds are broken, molecules can move out of fixed positions.

2008-09-04T07:17:00.000-07:00

UNIT 9:

- Thermal properties of matter

+ particles in a solid vibrate about fixed positions are held together by strong interatomic or intermolecular bonds.

+ total energy of these particles is called : INTERNAL ENERGY

internal energy comprises two components

----- kinetic energy-----

----- potential energy -----

** kinetic component

- due to vibration of the particles

- related to temperature

- higher temperature = more vigorous the vibrations

~ kinetic enegy is due to their movement instead of vibration

** potential component

- due to the stretching and compressing of intermolecular bonds as the particles vibrate

amount of potential energy stored in the bonds depends on the force between the particles and how far apart the particles are.

!! if the temperature of a substance rises, it is due to an increase in the average kinetic energy of its particles only.

potential energy is stores in the slinky as it is stretched or compressed, much like the interatomic or intermolecular bonds of particles.

a microwave oven raises the internal energy of food by making water molecules in the food vibrate vigorously.

2008-09-04T07:10:00.000-07:00

APPLICATIONS OF THERMAL ENERGY TRANSFER

---- common applications of radiation ----

1. vacuum flasks

2. shiny teapots

+++ why shiny teapots and not ordinary teapots?

-- shiny surfaces are bad emitters of radiation
-- shiny teapots can keep tea warm for a longer time
-- shiny containers can keep cold liquids cool for longer time

2008-09-04T06:58:00.000-07:00

APPLICATIONS OF THERMAL ENERGY TRANSFER

---- common applications of convection ----

1. refrigerators

2. electric kettles

3. air conditioners

2008-09-04T06:14:00.000-07:00

APPLICATIONS OF THERMAL ENERGY TRANSFER:

---- common applications of conduction ----

+ uses of good conductors of heat:

soldering iron rods

heat exchangers

cooking utensils

+ uses of bad conductors of heat

table mat

utensils handle

fibreglass

felt

sawdust

expanded polystyrene foam

wooden ladles

2008-09-04T05:40:00.000-07:00

radiation is different from conduction and convection.

+ RADIATION DOES NOT REQUIR A MEDIUM FOR ENEGRY TRANSFER.

- radiation can take place in a vacuum.

- thermal energy from infrared waves is called radiant heat.

the hotter the object, the greater the amount of radiant heat emitted.

*Infrared radiation is absorbed by all objects and surfaces.

*The absorption of radiation causes a temperature rise.

factors affecting rate of infrared radiation:

1. colour and texture

- dull, black surfaces are better emitters of infrared radiation.

2. surface temperature

- the higher the temperature of the suface of the object relative to the surrounding temperature, the higher the rate of infrared radiation.

3. surface area

- larger surface area will emit infrared radiation at a higher rate.

2008-09-04T05:00:00.000-07:00

convection currents occur only in fluids such as liquids and gases but not in solids.

- convection involves the bulk movements of the fluids

- those fluids carry thermal energy

For solids,
- thermal energy is tranferred from one particle to another through

VIBRATIONS.

- without any bulk movement of the particles themselves

Warm air rises and cool air sinks; a convection current forms in a room resulting from uneven heating and cooling

2008-09-04T04:36:00.000-07:00

difference between metal and non-metal.

metal contains many free electrons

they move randomly between the atoms or molecules

2. non- metals do not have free electrons

conduction in liquids and gases:

- particles in liquids and gases are spaced further apart

- collision between particles are less frequent in liquid

- collision between particles are even lesser in gases.

- transfer of kinetic energy in particles is slower

Therefore, air is a poor conductor of heat compared to water.

Therefore, air is a poor conductor of heat compared to most solids.

This experiment demonstrates that water is a poor conductor of heat. The ice at the lower part of the test tube does not melt quickly even when the water boils at the top.

2008-09-03T23:55:00.001-07:00

Heat can be transferred by one of three processes

Conduction

heat transferred by particles colliding into one another, such as in a metal; not important in the Sun.

Convection

heat transferred by the circulation of a fluid (or gas), such as in a heating system at home; important near the surface of the Sun.

Radiation

heat transferred by the flow of electromagnetic radiation, like heat felt from the campfire; important from the core to the surface of the Sun.

2008-09-03T23:48:00.000-07:00

http://spaceplace.nasa.gov/en/kids/st8/thermal_loop/index.shtml#

play this!!

2008-09-03T23:16:00.000-07:00

thermal energy is transferred by three processes:

conduction

- conduction is the process of thermal energy tranfer without any flow of the material medium.

convection

- convection is the transfer of thermal energy by means of currents in a fluid ( liquid or gases )

radiation

what's radiation?

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

2008-09-03T21:16:00.000-07:00

unit 8:

-transfer of THERMAL ENERGY

+ thermal energy always flows from a region of higher temperature to a region of lower temperature.

figure 8.1

this figure shows that the heat flows from a region of higher temperature to a region of lower temperature.

Have you ever wonder why do you feel the heat of the cup of hot coffee?
And why will the cup of ice tea heat up in your hands?

-that's because the heat from the coffee is flowing from the cup to your hands and

-the body heat will flow to the cup of ice tea and heat it up.

AMAZING ISN'T IT?

2008-09-03T21:08:00.000-07:00

this picture is rather blur.
but it can show that the molecule changes from the solid state to the gas state

when the temperature increases:
-a larger amount of thermal energy is converted to kinetic energy
-molecules to move faster.
- molecules overcomes the force of attraction
-able to move more freely
-molecules are moving faster and more freely
- changes its state from solid to liquid and lastly to gas.

2008-09-03T20:28:00.000-07:00

Brownian Motion !!!

- smoke particles move irregularly
- particles being bomnared by air molecules
- particles continually bombared unevenly on different sides
- bombaredment reasults in irregular movement

2008-09-03T06:09:00.000-07:00

the properties of solid liquid and gas.

qn 1: why can gas be compressed while solid and liquid can't?

- solid and liquids canot be compressed as their particles are closely packed

and there are little spaces inbetween.

whereas, gas has particles which are for apart

and there are alot of spaces inbetween them.

therefore, gas can be compressed and not solid and liquid.

qn 2: why does solid have fixed volume but not fixed shape?

- particles in a liquid are held by strong attractive forces

and are closely packed.

therefore, it has a fixed volume.

the particles are not in order,

hence, it does not have a fixed shape

2008-09-03T05:08:00.000-07:00

unit 7:

-kinetic model of matter.

arrangement of particles:
- particles CLOSELY packed together
- particles packed in an ORDERLY manner
- LITTLE space inbetween particles
- particles held together by STRONG forces
- particles vibrates about its FIXED position
- particles has LEAST energy
- HIGH density

arrangement of particles:
- particles CLOSELY packed together
- particles are NOT PACKED in an order
- LITTLE space inbetween particles
- particles held together by STRONG forces
- particles FREE to move
- particles has MODERATE energy
- relatively HIGH density

arrangement of particles:
- particles are FAR apart
- particles are in RANDOM position
- particles move FREELY
- particles held together by WEAK forces
- particles has MOST energy
- very LOW density