Physics!

chapter 9!

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

Internal energy-kinetc energy and potential energy
-Kinetic component is due to the vibration of the particles.
-Potential component is due to stretching and compressing of the intermolecular bonds as the particles vibrate.

Melting is when a solid changes to a lquid due to the temperature change.

melting point of ice where the constant temperature at which ice turns into the water(0 degrees celsius)
During the change of states from ice to water,there is no change in temperature even tough thermal energy is being absorbed.

Solidification is the change in state from liquid to solid,without a chanfge in temperature. Thermal energy is released by the substance.

Video:

Boiling-reverse of condensation. To determine the boiling point of any substance,continue heating until it boils. It is when a pure liquid is heated and changes to a vapour at a fixed or constant temperature.

How does a liquid boil?

the thermal energy is used to do work to separate the molecules as well as to push back on the surrounding atmosphere. The particles are now further apart with negligible intermolecular forces of attraction between them,thus there is a change in state from liquid to gas.

Evaporation

-Evaporationis like boiling where the change from liquids to gas takes place. However,evaporation can take place at any temperature.

differences between boiling and evaporation-

boiling:-

occurs at a fixed temperature
quick process
takes place throughout the liquid
bubbles form in the liquid
temperature remains constant
thermal energy supplied by energy source

evaporation:-

occurs at any temperature
slow procce
takes place only at the liquid surface
no bubbles are formed in the liquid
temperature may change
thermal energy supplied by the surroundings

evaporation removes thermal energy from surroundings.(eg. water)

how does evaporation occur?

Evaporation of ether takes place at room temperature where energetic molecules are able to escape from the liquid surface.

Application of evaporation

1.evaporation on skin

2.wet clothes dry after a while

3. person with fever can be controlled and kept down trough water

4.the refrigerator keeps the contents in the fridge cold.

FACTORS!

-temperature-higher temperatures increases the rate of evaporation. A warmer liquid has greater number of molecules at the surface layer.

-humidityof surrounding air-rate of evaporation decreases with increasing humidity

surface area of liquid-A larger exposed surface area means more molecules can escape from the liquid.

-movement of air-moving from one's hair dryer removes the molecules of a liquid as oon as they escape from the surface of hair.

-pressure-reducing the atmospheric pressure increases the rate of evaporation

-boiling point of the liquid-liquids with lower boiling point will evaporate faster.

Done! :D

Chapter 8!

2008-09-05T04:22:00.000-07:00

-Thermal energy always flow from a region of higher temperature to a region of lower temperature.

-Thermal energy can be transferred by:-conduction,convection and radiation.

-When thermal equilibriumis reached between two bodies.there is no net flow of thermal energy between them.

what is conduction?

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

Thermal energy flows through the material of each rod without any flow of the material iself. Such a transfer of thermal energy without any movement of the material medium is called conduction.

Different materials conduct heat at different rates.

-a poor conductor of heat is insulation.

what is a convection?

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

-a convection current is the movement of fluid caused by the change in density in various parts of the fluid.

WHAT IS A radiation?

-Radiation is the continual emission ofinfrared waves fromthe surface of all bodies,transmitted without the aid of a medium.

-Absorption radiation is absorbed by all objects and surfaces.(causes a rise in temperature.)

-emission by all objects and surfaces where it causes temperature of the object themselves to fall.

-a good emitter of a radiant heat is also a good absorber of radiant heat.

Factors affecting rate of infrared radiation

colour and texture of the surface

black surfaces are better absorbers og infrared radiation.

surface temperature

the higher the temperature of the surface of the object relative to the surrounding temperature, the higer the rate of infrared radiation

surface area

the object with the larger surface area will emit infrared radiation at a higher rate

applications of conduction

uses of good conductors of heat:

-cooking utensils

-soldering iron rods

-heat exchangers

insulators of heat:

-handles of appliances and utensils

-table mats

-sawdust

-wooden ladles

-woollen clothes

-fibre glass, felt and expanded polystyrene foam

common applicatons of convection

1. electric kettle- the heating coil of an electric kettle is placed at the bottom to aid transfer of thermal energy in water by convection

2. household hot water system

3. air-conditioner - the air is recirculated and the temperature of the air will eventually fall to the desired level

4. refrigerator - the convection of currents inside the refrigeration cabinet help cool the contents inside

common applications of radiation

1. teapots - shiny containers can keep cold liquids cool for a longer time than black containers

2. the greenhouse - the infrared radiation emitted by the contents in the greenhouse is different compared to the infrared radiation emitted by the sun. the infrared radiation emitted by the contents gets trapped. the amount of infrared radiation builds up over time, causing the temperature to increase

3. vacuum flask-designed to keep liquids hot by minimising heat loss through radiation,evaporation,conduction and convection.

Done! :D

Chapter 7

2008-09-03T17:25:00.000-07:00

there are 3 different states of matter-solid,liquid and gas.

properties of solid:-

fixed shape and volume
hard and rigid
high density
incompressible

properties of liquid-

fixed volume but no fixed shape
high density
incompressible

properties of gas-

no fixed shape or volume
low density
compressible

Kinetic model of matter

All matter are made up of tiny paricles called atoms or molecules(chemistry) and are always in motion.

arrangement of particles in solid-

closely packed and in a regular pattern;high density

movement-

vibrate about fixed position only and is held in position by intermolecular bonds;fixed volumes and shapes.

arrangement of particles in liquid-

randomly arranged,and are further apart;high density

movement-

free to move about and have attractive forcedbetween particles;fixed volume but no fixed shape.

arrangement of particles in gas-

very far apart and occupies any space available;low density

movement-

little attraction and move randomly at very high speeds;no fixed volume and shape but highly compressible

strength of intermolecular force(weak to strong) :gas,liquid,solid

relative distance between particles(close to far apart) :solid,liquid , gas

Brownian motion is the random or irregular motion of smoke particles in air(occurs only in fluids)

Effects of temperature on molecular motion:

-higher temperature-particles becomes more vigorous and agitated(vice versa),but WHY?

this is because particles hit one wnother vigoruously and frequently. Air molecules have greater speeds at higher temperaures. When temperature increases,a larger amount of thermal energy is converted to kinetic energy of air molecules.

Brownian Motion:

Done! :D