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 Eileen Chia(9) This is a Physics blog 3B2 Tagboard Links and Credits linkone linktwo Layout: hearteditorials Codes: -ambulance Icon: biconcave |
Thursday, September 4, 2008
WHEEEEEEEE! I'M DONE WITH MY PHYSICS BLOG! EVERYONE SAY YAY! HAHA!
 A nice star for my work:D Heh. Kidding! Everyone! Hurry go do your physics blog:D Chapter 9: Thermal Properties of Matter Internal Energy Total energy of the particles. It comprises of two componenets - kinetic energy & potential energy. The kinetic component of internal energy is due to the vibration of the particles. It is directly related to temperature. The higher the temperature, the more vigorous the vibrations of the particles. In liquids and gases, the particles are able to move freely. Thus, the kinetic energy is due to their movement instead of vibrations. The potential component of internal energy is due to the stretching and compressing of the intermolecule bonds as the particles vibrate. The amount of potential energy stored on the bonds depends on the force between the particles and how far apart the particles are. Therefore, we can see that if the temperature of the substance rises, it is due to and increase in the average kinetic energy of its particles only. Melting and Solidification Melting When a solid changes to a liquid upon heating, this change of state is called melting. For a pure substance, melting occus at a definite or constant temperature. This particular temperature is known as the melting point of the substance. Solidification The reverse process of melting is called solidification - changing from a liquid to a sold. A pure substance will solidify or freeze at a temperature equal to its melting point. For example, water freezes to form ice at 0 degree celsius. We call this temperature of 0 degree celsius the freezing point of water. Boiling and condensation When a pure liquid is heated and it changes to a vapour at a fixed or constant temperature, we call this change of state boiling. This particular temperature is known as the boiling point of the substance.The reverse of boiling is condensation. It is the change of state from vapour to liquid when a substance is cooled at the same constant temperature as in boiling. -During boiling, the temperature remains constant at its boiling point. thermal energy is being absorbed by the substance. Evaporation Evaporation is the change of state from liquid to gas. The different between boiling and evaporation is that evaporation can occur at any temperature. Boiling 1. Occurs at fixed temperature 2. quick process 3.Takes place throughout the liquid 4.Bubbles are formed in the liquid 5.Temperature remains constant 6.Thermal energy supplied by an energy source Evaporation 1. Occurs at any temperature 2. Slow process 3. Takes place only at liquid surface 4. No bubbles formed in the liquid 5. Temperature may change 6. Thermal energy supplied by the surroundings Factors affecting the rate of evaporation: 1) Temperature Raising the temperature of the liquid will increase the rate of evaporation. A warmer liquid means that a greater number of molecules at the surface layer are energetic enough to escape. 2) Humidity of the surrounding air The rate of evaporation decreases with increasing humidity. Wet clothes do not dry easily if the surrounding air is damp. Wet floors take a longer time to dry on a humid day. Similarly, the rate of evaporation increases with lower humidity. 3) Surface area of the liquid The rate of evaporation increase when there is more exposed surface are of the liquid. This is because evaporation only takes place at the exposed surface of a liquid. A larger exposed surface area means more molecules can escape from the liquid. 4) Movement of air The rate of evaporation increases when the surrounding air is moving. 5) Pressure Reducing the atmospheric pressure increases the rate of evaporation. 6) Boiling point of liquid Liquids with lower boling points will evaporate faster. END OF CHAPTER NINE :D TADAAAAAAAAA Chapter 8: Transfer of Thermal Energy - Thermal energy is transferred only when there is a difference in temperature. - Thermal energy always flows from a region of higher temperature to a region of lower temperature. Thermal energy is transferred by any of these three processes;
1. Conduction Conduction is the transfer of energy from one molecule to another. This transfer occurs when molecules hit against each other, similar to a game of pool where one moving ball strikes another, causing the second to move. Conduction takes place in solids, liquids, and gases, but works best in materials that have simple molecules that are located close to each other. For example, metal is a better conductor than wood or plastic. Conduction is the process of thermal energy transfer without any flow of the material medium. 2. Convection Convection is the movement of heat by a liquid such as water or a gas such as air. The liquid or gas moves from one location to another, carrying heat along with it. This movement of a mass of heated water or air is called a current. Convections requires the movement of particles, so it can only take place in liquids and gases. Convection is the transfer of thermal energy by means of currents in a fluid (liquids or gases) 3. Radiation Heat travels from the sun by a process called radiation. Radiation is the transfer of heat by electromagnetic waves. When infrared rays strike a material, the molecules in that material move faster. In addition to the sun, light bulbs, irons, and toasters radiate heat. When we feel heat around these items, however, we are feeling convection heat (warmed air molecules) rather than radiated heat since the heat waves strike and energize surrounding air molecules. Radiation is the continual emission of infrared waves from the surface of all bodies, transmitted without the aid of a medium. Unlike conduction and convection, radiation does not require a medium for energy transfer. This means that radiation can take place in a vacuum. Factors affecting the rate of infrared radiation Rate of infrared radiation depends on three factors:
Applications of Thermal Energy Transfer Uses of good conductors of heat If thermal energy has to be transferred quickly through a substance, good conductors of heat such as metals are used. Some examples of the uses of metals are: 1. Cooking utensils like kettles, suacepans and boilers. They are usually made of stainless steel where direct heating is involved. 2. Soldering iron rods are made of iron with the tip made of copper, as copper is a much better conductor of heat than iron. 3. Heat exchanges, such as those used in a large laundry facility, help save energy. Uses of bad conductors of heat (Insulators) Insulators are very useful if we want to minimise loss of thermal energy, or prevent thermal energy from being transferred quickly. Some common uses of insulators are: 2.Tables mats are usually made of cork so that hot kitchenware can be placed on them without damaging the tabletop 3. Sawdust is used to cover ice blocks to reduce melting because of its good insulating property. 4. Wooden ladles are very useful for stirring or scooping hot soup and also for scooping rice that has just been cooked 5. Woolen clothes are used to keep people warm on cold days. 6. Fiberglass, felt and expanded polystyrene foam which trap large amounts of air are employed as insulators in the walls of houses, ice boxes and refrigerators.
Common applications of radiation
END OF CHAPTER EIGHT :D Wednesday, September 3, 2008 Chapter 7: Kinetic Model of Matter Matter is commonly defined as the substance of which physical objects are composed, not counting the contribution of various energies or force fields, which are not usually considered to be matter per se (though they may contribute to the mass of objects). Matter constitutes much of the observable universe, although again, light is not ordinarily considered matter. Unfortunately, for scientific purposes, "matter" is somewhat loosely defined. It is normally defined as anything that has mass and takes up space. Matter (energy) can be in several different states, the most common being high energy physics, solids, liquids and gases. Anything which both occupies space and has mass is known as matter. In physics, there is no broad consensus as to an exact definition of matter, partly because the notion of "taking up space" must be ill-defined for quantum reasons. Physicists generally do not use the saying when precision is needed, preferring instead to speak of the more clearly defined concepts of mass, energy and particles.  SOLID Arrangement of particles: - Closely packed together, usually in a regular pattern, occupying minimum space - Results in solids having high densities Movement of particles: - Vibrate about fixed positions only. Held in position by very strong intermolecular bonds - Explains why solids have fixed volumes and shapes LIQUID Arrangement of particles: - Randomly arranged with the particles slightly further apart as compared to that of solids - Results in liquids having relatively high densities Movement of particles: - Free to move about but confined within the vessel containing it. Have attractive forces between particles - Explains why liquids have fixed volumes but will take the shape of vessels containing them GAS Arrangement of particles: - Very far apart. Particles are randomly arranged and will occupy any available space - Results in gases having low densities Movement of particles: - Particles have very little attraction between them and move about randomly at very high speeds - Explains why gases have no fixed volume and shape, and why they are highly compressible *There are more than 3 states of matter, but most people only know the gaseous, liquid and sold states. One other well-known state of matter is plasma, found in plasma televisions or plasma spheres. BROWNIAN MOTION  Brownian motion: - Random or irregular motion of smoke particles in air - Occurs only in fluids Effects of Temperature on molecular motion - The higher the temperature, the more vigorous and agitated the motion of smoke particles get - The lower the temperature, the less vigorous and agitated the motion of smoke particles will be Why is this so? Air molecules are bombarding the smoke particles more vigorously and frequently. This means that air molecules have greater speeds at higher temperatures. When the temperature increases, a larger amount of thermal energy is converted to kinetic energy of the air molecules. This will cause the molecules to move faster. END OF CHAPTER SEVEN :D  Physics is the study of the natural world around us - from the very large, such as the solar system, to the very small, such as the atom. The study of physics is commonly divided into major topics such as General Physics, Thermal Physics, Light, Waves and Sound, Electricity and Magnetism. All these topics are related to two main ideas: matter and energy. However, this blog will only cover thermal physics, which is chapter 7, 8, 9 of the textbook.
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