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2008-09-05T20:46:00.000-07:00

VIDEO!!

SONG about Physics

Evaporation & Condensation

Conduction

Convection

Molecules in Soid

Molecules in Liquid

2008-09-05T08:49:00.000-07:00

EVAPORATION

drying of hair

movement of paricles during evaporation

puddle of water evaporating

CONDENSATION

condensation occuring on a cup

changing of state [gas => liquid]

BOILING

boiling point

boiling of water

MELTING

ice cube changing its state

melting point

SOLIDIFICATION

candle wax solidifying

a cup of water freezing

change in movement of particle during freezing

2008-09-05T07:40:00.000-07:00

CHAPTER 9

- Temp is the degree of HOTNESS and COLDNESS of a body
!!! Heat is the amount of thermal energy flowing from HOTTER region to COLDER region

~ Internal energy is the total energy of the particles held by strong bonds
- potential energy & kinetic energy

KINETIC COMPONENT

--> due to vibration of particles
--> the higher the temp, the more vigorous vibration is
--> in liquid / gas, particles move. thus, KE is due to movement

POTENTIAL COMPONENT

--> due to stretching / compressing of bond as particles vibrate
--> amt stored in bond depends on force between particles and how far they are

Melting & Solidification
+ solid => liquid: MELTING
+ melting occurs at a certain temp, it is the MELTING POINT
+ melting pnt: 0 degree celcius [ice => water]
+ when bonds are broken, melting occurs
+ hence, the molecules are able to move out of their fixed positions
+ liquid => solid: FREEZING / SOLIDIFICATION

Boiling / Condensation
+ liquid => gas: BOILING
+ the temp where it boils is called BOILING PNT
+ boiling point: 100 degree celcius [water => steam]
+ molecules move apart, boiling occurs
+ gas => liquid: CONDENSATION
+ thermal energy is given out

Evaporation
+ liquid => gas: EVAPORATION
!!! evaporation occurs at ANY temperature
+ thermal energy is carried away
+ collision of air molecules rebounds some molecules
+ occurs at SURFACE of water

~ experience cooling effect on skin
~ puddle of water dries up
~ lowers temp

FactorS AffectinG RatE Of EvaporatioN

1. Temperature
- rise of temp increases rate of evaporation

2. Humidity of surrounding air
- increasing rate of evaporation decreases rate of evaporation
- rate of evaporation increases with lower humidity

3. Surface area of liquid
- larger surface area, rate of evaporation increases
- more molecules escapes with larger exposed area

4. Movement of air
- moving of air remove molecules of liquid when they escape from the surface
- rate of evaporation increases when surrounding air is moving

5. Pressure
- reduced in pressure increases rate of evaporation

6. Boiling point of liquid
- liquids with LOWER bp evaporates FASTER

2008-09-05T06:53:00.000-07:00

CHAPTER 8

Common Applications of Convection

1. Electric Kettles

+ heating coil is placed at the bottom to help in transfer of energy in water by convection

+ when power is switched on, water is heated

+ it expands and become less dense

kettles

2. Household Hot Water Systems

3. Air Conditioners

+ the rotary releases cool dry air

+ cool air is denser hence it sinks

+ warm air being less dense is drawn to where is cooled

+ air is recirculated, temp falls

air conditioners

4. Refrigerators

+ freezing unit placed at the top to cool air and facilitate sets up convection currents

Common Applications of Radiation

1. Teapots

+ shiny surface are BAD emitters of radiation

+ shiny teapots keeps the tea warm and they are BAD absorbers of radiation

+ it can also keep cold liquid cool

shiny teapots

2. Greenhouse

+ help plants to grow better by trapping heat during cold weathers

+ during the day, infrared radiation warms the soil and plants

greenhouse

3. Vacuum Flasks

+ helps to keep liquid hot

+ minimises heat loss through CONDUCTION, CONVECTION, RADIATION, EVAPORATION

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Factors which affects RATE OF INFRARED RADIATION

1. Colour / texture of surface

BLACK- better absorbers, emitters of infrared radiation

2. Surface Temperature
~ higher temp of surface relative to surrounding temp, the higher rate of infrared radiation

3. Surface Area

~ object with larger surface area, emits infrared radiation at higher rate

USES OF GOOD CONDUCTORS OF HEAT

1. Cooking Utensils

+ direct heating is involved

frying pan

cooking pot

saucepan

kettle

2. Soldering Iron Rods

+ copper is a better conductor of heat than iron

3. Heat Exchangers

+ save energy

USES OF BAD CONDUCTORS OF HEAT

1. Handles of Appliances or Utensils

+ hot surfaces can b picked without scorching our hands

teapot

handle of saucepan

2. Table Mats

+ can be placed on without damaging tabletop

table mat made of cork

3. Sawdust

+ cover ice block to reduce melting

sawdust

4. Wooden Ladles

+ for scooping or stirring hot soup

wooden ladles

ladle

5. Woollen Clothes

+ to keep people warm duing cold days

woolleen clothes

6. Fibreglass, felt, Poylstyrene foam
+ trap large amt of air

fibreglass

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ThErMaL EnErGy

+ transferred ONLY when there is a difference in temp

!!! flows from region of HIGHER temp TO region of LOWER temp

--> THERMAL EQUILIBRIUM:no gaining or losing of thermal energy

transferred through CONDUCTION, CONVECTION, RADIATION

ConductioN

!!! a process whereby thermal energy is transferred without flow of any material medium

the words are kind of BLUR

- different materials conduct heat at different rates

- METALS are good conductors of heat

- NON-METALS are poor conductors of heat [insulators]

IN SOLIDS

- tiny particles culd be found in ALL solids [atoms, molecules]

- metal contains many free electrons

- non-metals does not contain any of it

+ particles at hot end vibrates vigourously, colliding with other particles causing it to vibrate as well

+ when metals are heated, the free electrons in it gain KE and so it moves faster

+ those electrons as a result diffuse / spread to cooler parts

frying of egg involves conduction!! WOW! =)

IN LIQUIDS / GAS

~particles are further apart so there collisions of particles are LESS frequent

~ transfer of KE is slower

POOR conductor of heat

ConvectioN

!!! transfer of thermal energy by means of currents in ONLY fluid [liquid, gas]

- involves movement which carries thermal energy

-for SOLID, thermal energy is transferred from one particle to another through VIBRATION

+ when water is heated, it expands

+ it is less dense than surrounding water therefore it rises

+ cooler region is denser therefore it sinks

RadiatioN

!! continual emission of infrared waves from surface of ALL bodies, transmitted without medium

- can take place in vacuum

- thermal heat from infrared waves is called RADIANT HEAT

2008-09-05T02:53:00.001-07:00

Chapter 7 [Kinetic Model Of Matter]

BROWNIAN MOTION

- irregular motion of smoke particles in the air

- occurs only in fluid that has ability to flow / particles that are able to move freely [gas, liquid]

-->smoke particles at higher temp causes the motion of smoke particles to be more vigorous and air molecules move at greater speed

--> air molecules bombard smoke particles more vigorously

--> larger amt of thermal energy is converted to KE when temp increases, hence, molecules move faster

chapter SEVEN

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SOLID

+ fixed shape
+ fixed volume
+ high density
+ hard
+ densed
+ incompressible

+ closely packed
+ arranged in an orderly manner
+ occupy little space

+ vibrate about fixed position
+ held by strong forces
+ least energy in particles

LIQUID

~ NO fixed shape
~ fixed volume
~ high density
~ soft
~ CANNOT be compressed

~ closely packed
~ not in an orderly manner
~ randomly arranged

~ moves about freely
~ held by strong forces
~ moderate energy

GAS

- NO fixed shape
- NO fixed volume
- NOT densed
- can be compressed

- far apart
- NO pattern
- positioned randomly

- move randomly
- freely and at a high speed
- held by weak forces
- A LOT of energy in the particle