amandER Liew's physics blog

2008-09-05T02:23:00.000-07:00

LAST CHAPTER!
CHAPTER 9 - THERMAL PROPERTIES OF MATTER!

SO!

WHAT IS INTERNAL ENGERGY?
- Internal energy is actually, the energy found in the particles that causes them to vibrate :D
- internal energy comprises both K.E. and P.E. (in case you don't know what it is, -.- it's kinetic energy and potential energy!)

Kinetic energy of internal energy is due to the vibration of the particles.
- the higher the temperature, and more vigorous the movements
- in fluids (liquids and gases) K.E. is due to movement

Potential energy of the internal energy is due to the stretching and compressing of the intermolecular bonds (a force that holds particles in solids together) as the particles vibrate
- P.E. stored depends on the force between particles and how far they are from each other :D

Melting and Solidification

Melting:
-When a solid, when heated,changes to a liquid, the change of state (from solid to liquid) is called melting!
- melting occurs at a constant temperature in pure substances (it's called the melting point)

How do solids melt? hmm..
In order for a solid to melt, intermolecular bonds within the solid must be broken.
Since ENERGY is need to break the bonds,
thermal ENERGY is supplied for a period of time for the intermolecular bond to break
Once the intermolecular bonds have broken, the particles can move freely (in liquid state).

Solidification
It's the reverse of melting!
- when liquids becomes a solid again.
- a PURE substance will freez at the temperature equal to it's melting point
- we call that temperature the freezing pont as well.

OOOOOOOOOOHHHHHHH frozen water is COOL...
literally.

BOILING
When a PURE substance changes from liquid to a vapour at a fixed temperature, the process is called boiling and the temperature of which it changes state is called the boiing point.

CONDENSATION
It the reverse of BOILING. It changes state (from gas to liquid) at the same temperature as it's boiling point. Thermal energy is given off.

How does a liquid boil?
Thermal energy causes the molecule to be further apart with negligile intermolecular frces between the particles. When this happens, a change of state (liqud to gas) occurs.

EVAPORATION
Evaporation is like boiling. It is when liquid changes state and becomes gas.

THE DIFFERENCE BETWEEN EVAPORATION AND BOILING!
- NUMBER ONE!: Boiling occurs at a FIXED temperature but evaporation occurs at ANY temperature.
- NUMBER TWO!: boiling is a quick process, evaporation is SLOW....
- NUMBER THREE!: boiling takes place THROUGHOUT the liquid, evaporation takes place only on the surface of the liquid
- NUMBER FOUR!: bubbles ar formed in the water duing boiling, and none are formed in evaporation
- NUMBER FIVE!: temperature remains constant in boiling and temperature might change in evaporation
- NUMBER SIX!: in boiling, thermal energy is supplied by the energy source, whereas in evaporation, therma enery is supplied by the surrounding temperatures

more bout evaporation:
EVAPORATION CAUSES COOLING!
When water evaporates from your skin, thermal energy is taken away as well.
And therefore your body cools....

How does evaporation occur?

It occurs when energetic molecules overcome the downward attractive forces of other molecules and escape. Carrying with it thermal energy.

APPLICATION of EVAPORATION
- when perspiration evaporates off your skin
- wet clothes or puddles of water dry off after some time
- when a person has a fever, the person is sponged with water. when water evaporates from the person's skin, heat will be slighly removed.
- refrigerators use the concept of condensation and evaporation to keep its things cool

Factors that effect evaporation
1. TEMPERATURE (the higher the temp, the higher the rate of evaporation)
2. HUMIDITY OF THE SURROUNDIND AIR (the higher the humidity, the lower the rate of evaporation)
3. SURFACE ARE OF THE LIQUID (the bigger the surface area, the higher the rate of evaporation)
4. MOVEMENT OF AIR (the higher the movement in air, the higher the rate of evaporation)
5. PRESSURE (the lower the pressure, the higher the rate of evaporation)
6. BOILING POINT OF THE LIQUID (the higher the temp, the lower the rate of evaporation)

video time!

hahahha enjoy!

that's all for chapter 9!
*cheers*
here's something to laugh at.

hahahahah lecturers are awesome!
HOLLA!

2008-09-04T23:23:00.000-07:00

CHAPTER 8 - TRANSFER OF THERMAL ENERGY

NOTE!
- Thermal energy is transferred only when there is a difference in temperature
- Thermal energy always flows from a region of hgher temperture to a region of lower temperature

HOW IS THERMAL ENERGY TRANSFERRED?

Energy can be transferred in 3 ways: conduction, conection and radiation.

Conduction

Definition:
Conduction is ather process of thermal energy transfer without any flow of the material medium

Eg. when one end of a metal rod is heated,
the other end will soon be heated up as well.
this shows that energy is transferred.

HEAT IS TRAVELLED THROUGH A MEDIUM IN CONDUCTION!

Different materials conduct heat at different rates.
Metals such as copper, siver and iron are good conductors of heat.
Non-metals such as glass, plastic, water and even air are insulators (or poor conductors) of heat

and HOW DOES CONDUCTION WORK?
the difference between metals and non-metals is that metals have spare electrons and non-metals don't.
the SPARE/FREE electrons move freely and randomly between atoms.

When an atom in metals vibrate, the free electrons gains kinetic energy and causes the other atoms to vibrate as well, causing heat to be transferred at a greater speed as when compared to non-metals.

CONDUCTION in liquids and gases

The particles in gases and lquids are spaces further apart as when compared to that in solid, therefore there is lesser collision in liquids and lesser in gases.
The Transfer of kinetic energy from fast-moving particles to neighbourin particles are slower and that's why air is a better insulator as compared to water.

Convection

Definition:
Concection is the transfer of thermal energy by means of currents in a fluid (eg. liquids and gases)

HOW DOES CONVECTION WORK?
Convection can only work in FLUIDS! sch as liquids and gases.
(not in solids).

i actually found the same video a CHARA!

but here's something that we can use in our everyday life about how convectin currents affect global warming.

Radiation

Definition:
Radiation is the continual emission of infraread waves from the surfec of all bodies transmitted without the aid of a medium

OOH! same picture as chara again :D

-Radiation DOES NOT require a medium for energy tranfer!
- meanig, radiation can take place in a vacuum
- eg. thermal energy reach the Earth from the Sun through radiation.
- convection and conduction cannot be performed because there is no medium.

Thermal heat from Infrared waves(EM waves) are called radiant heat.
the hotte an object, the greater the amount of radiat heat.
The absorption of radiat heat causes the temperature in an object to increase.

Factors that affect the rate of infrared radiation
- Colour and textre of the surface
- Dull surfaces absorb radiation better than shiny white surfaces.
- Dull surfaces are also better emitters of infrared radiation

- Surface temperature
- The higher the temperature of the surface of the object
relative to the surrunding temperature, the higher the radiation.
- meaning: the higher the surface temperature as compared
to the surrounding temp.

- Surface area
when 2 objects with the same material andmass but different surfaces area, the one with the larger surface area will emit infrared radiation at a higher rate.

ALRIGHT! LAST PART!

Applications of thermal energy transfer!

for CONDUCTION:
- cooking utensils such as kettles, saucepans and boilers are made of aluminiu or stainless steel due to direct heating

- Soldering iron rods are made of iron with copper tips as copper is a better conductor of heat than iron
- SOLDERING: is a process in which two or more metal items are joined together by melting and flowing a filler metal into the joint.
- you can use soldering for electric guitar strings! that's what my friend does :D

INSULATORS!
- handles of kettles and saucepans
- table mats (to prevent damaging or table tops)
- sawdust (to cover ice blocks to prevent it from melting)
- Wooden ladles (for stirring or scooping hot food)
- Woollen clothes (for cold days)

for CONVECTION:
- electric kettles (heating coil causes convection currents)
- household water systems (designed based on convection in liquids)
- everyone's favourite AIR-CONDITIONERS
- refrigerators (cool air comes down and heat goes up!)

for RADIATION:
- Teapots (shiny surfaces keeps heat IN)
- Greenhouses (shiny glass traps heat in greenhouses and allows heat to go in)
- Vacuum Flask (deisgned to minimise heat loss)

THAT'S ALL FOLKS!
FOR CHAPTER 8!
HOLLA!

2008-09-04T21:07:00.000-07:00

hello all!
today, i'll be blogging about
CHAPTER 7 - KINETIC MODEL OF MATTER

7.1
we recap on the different properties ofthe different states of matter:
Matter can exist in 3 different states; solid, liquid and gases.

Solids have stable and a definite shape and volume. They cannot change in shape unless a force is applied to it (such as when being broken or cut). In solids, particles are packed closesly together and cannot move freely. They can only VIBRATE at a fixed position. The movement of energy and temperature is LOW.

Liquids do not have definite shapes. Their shapes are determined by the containers they are contained in. Liquids have definite volumes. The particles are farther apart than that in a solid therefore can slide past each other easily. The movement of energy and temperature is therefore HIGHER then solids

Gases have BOTH indefinite volumes and indefinite shapes. Because the particles in gases are so far apart, they can be compressed and therefore they do not have fixed volumes. They can also move about freely and quickly. The movement energy and temperature is HIGHER than both solids and liquids.

BROWNIAN MOTION

The Brownian motion is a random or irregular motion of smaoke particles in the air.
IT CAN ONLY OCCUR IN FLUIDS (which is a substance that has freely moving particles or the ability to flow)!

the surrounding temperature effects the Brownian motion!
high temperatures: smoke praticles will become vigorous
low temperatures: there is less movement

WHY SO?
When temperature increses, more thermal energy is converted to kinetic energy of air molecules.
This will couse the molecules to move FASTER!

that's all!
HOLLA!