Physics Blog

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

Chapter 9

Continuing thermal energy.. (:

Temperature and internal energy
- Total energy of interatomic ot intermolecular bonds is called internal energy.
- Internal energy is made up of kinetic energy and potential energy.
- The kinetic component of internal energy is due to the vibration of the particles.
- The potential component of internal energy is due to the stretching and compressing of the intermolecular bonds as the paricles vibrate.
- An increase in temperature leads to an increase in the kinetic component of the internal energy.
http://www.youtube.com/watch?v=6tO4VvcEChk

Melting
- Melting is the change of state from solid to liquid, without a change in temperature.
- For pure subtance, melting occurs at a definte or constant temperature, known as melting point of the substance.
- When solid melt to ice, the strong molecular bond is broken.
- During melting, the temperature remains constant at the melting point, hence, thermal enregy is absorbed by the substance.
http://www.youtube.com/watch?v=YQ7TFeqnW0o

Solidification and freezing point
- Solidification is the change of state from liquid to solid,without a change in temperature.
- For pure substance, it willl solidify or freeze at the same temperature as the melting point, also known as freezing point.
- During solidification, the temperature remains constant at the freezing point, hence, thermal energy is released by the substance.
http://www.youtube.com/watch?v=DZ9wlQ5MCnU

Boiling
- Boiling is the change of state from a liquid into vapour, occuring at a constant temperature.
- The contant temperature is called boiling point.
- During boiling, the temperature remains constant at its boiling point, hence, thermal energy is absorbed by the substance.
http://www.youtube.com/watch?v=zFj_i6HtebM

Condensation
- Condensation is the change of state from vapour to liquid when a substance is cooled at the same constant temperature as in boiling.
- During condensation, the temperature remains constant at the condeation point, hence, thermal energy is released by the substance.
http://www.youtube.com/watch?v=6dpC_oNrIM0

Evaporation
- Evaporation is a cooling process.
- Evaporation can occur at any temperature.
- Evaporation requires thermal energy in the urrounding, causing cooling.
- Temperature, humidity of the surrounding air, surface area of the liquid and movement of air are the factors affecting the rate of evaporation.
http://www.youtube.com/watch?v=yyxc-81JDbo

Applications of evaporation
1. Experience cooling effect.
2. Wet clothes or puddle of water dry up after a while.
3. Keeps fever patient's temperature down.
4. Cooling process keep the food in the refrigerator cold.

Credits:
http://www.youtube.com/ (:

2008-09-05T06:01:00.000-07:00

Chapter 8

In this big chapter, it's all about thermal energy.

Uses of thermal energy, transfer of thermal energy and many more.

I'll add a video for better understanding as this post seem so wordy. :P

Transfer of thermal energy

- It only takes place when there is a difference in temperature.

- It always flow from a region of higher temperture to a region of lower temperature.

- There is no net flow of thermal energy between them, hence, thermal equilibrium is reached between 2 bodies.

- 3 processes of thermal energy transfer: conduction, convection, radiation.

http://www.youtube.com/watch?v=y5elZN-Mp4w

1. Conduction

- Conduction is the process of thermal energy transfer without any flow of the material medium.

- Different materials conduct heat at different rates as different material usedifferent mechanisms for transferring thermal energy.

- The 2 mechanisms for conduction are atomic or molecular vibrations (metals and non-metals) and free electron diffusion(only metals).
- Compared to solid, liquid and gas are poor conductors of heat.

http://www.youtube.com/watch?v=oWjDnNr5T6A

2. Convection

- Convection is the trnasfer of thermal energy by means of current in a fluid(liquid or gases).

- Convection currents occur only in fluids such a liquids and gase but not in solids.

- For solid, the thermal energy is transferred from one particle to another through vibration, without any bulk movement of the particle itself.

http://www.youtube.com/watch?v=xnB-Y8wPK2w

Common applications of convection:

1. Electric kettles

2. Household hot water systems

3. Air conditioners

4. Refrigerators

3. Radiation

- Radiation is the continual emission of infared rays from the surface of all bodies, transmitted without an aid of a medium.

- Thermal energy from infared rays is called radiant heat.

- It is absorbed by all objects and surfaces causing a temperature rise.

- It is emitted by all objects and urfaces causign the temperature to fall.

- Colours and texture of the surface, surface temperature and surface area are factors affecting rate of infared radiation.

http://www.youtube.com/watch?v=YEoLzKZ0nrs

Common applications of radiation:

1. Teapots

2. The greenhouse

3. Vacuum flasks

Uses of good conductor of heat

1. Cooking utensils

2. Soldering iron rods

3. Heat exchangers

Uses of bad conductors of heat

1. Handles of appliances and utensils

2. Table mats

3. Sawdust

4. Wooden ladles

5. Woollen clothes

6. Fibreglass, felt and expanded polystyrene foam

I've found a website on the same topic.

Go have a look when you have time. (:

http://www.phy.cuhk.edu.hk/contextual/heat/tep/trans01_e.html

Credits:

www.youtube.com (:

www.google.com (pictures) (:

2008-09-04T10:38:00.000-07:00

Chapter 7

Finish reading on chapter 7.
Going to summarize as to easier studying in the future. (:

All substances exist in 3 states
3 States of matter- Solid, Liquid & Gas

Properties:
Solid
-Fixed shape & volume
-Hard & rigid; Hard force needed to change its shape
-High denstiy

Liquid
-Fixed volume but does not have fixed shape
-High density

Gas
-No fixed shape or volume
-Low density

Example:
Water has 3 states of matter.
It exist as snow & ice cube in solid state.
It exist as water in liquid state.
It exist as steam in gaseous state.

Kinetic model of matter-Asumption of tiny particles in continuous motion

Model of solid

1. Closely packed together in a regular pattern
- Vibrate in fixed positions, held by very strong intermolecular bonds
2. Results in high density
- Explaining why solids have fixed volume & shape

Model of liquid

1. Randomly arranged, slightly further than in solid
- Free to move but still confined, held by attration forces
2. Results in having relatively high densities
- Explaining why liquids only have fixed volume and not shape

Model of gas

1. Very far apart, randomly arranged
- Have little attraction and move about randomly
2. Results in having low densities
- Explaining why gas have no fixed volume or shape

http://www.youtube.com/watch?v=s-KvoVzukHo&feature=related
Found this video on youtube and might bring us more understanding
To 3 states of matter. (On both Chemistry and Physics)

Credits: