Heat Transfer PDF

HEAT TRANSFER UNSCRAMBLE THE LETTERS UILDF DIOANATIR CKLBA YBDO VONCOECTIN RCDNTCOOU  Question ► If a cup of coffee and a red popsicle were left on the table in this room what would happen to them? Why?  Question ► Ifa cup of coffee and a red popsicle were left on the table in...

HEAT TRANSFER UNSCRAMBLE THE LETTERS UILDF DIOANATIR CKLBA YBDO VONCOECTIN RCDNTCOOU  Question ► If a cup of coffee and a red popsicle were left on the table in this room what would happen to them? Why?  Question ► Ifa cup of coffee and a red popsicle were left on the table in this room what would happen to them? Why? ✔ The cup of coffee will cool until it reaches room temperature. The popsicle will melt and then the liquid will warm to room temperature. Heat Transfer ►Heat always moves from a warmer place to a cooler place. ►Hot objects in a cooler room will cool to room temperature. ►Cold objects in a warmer room will heat up to room temperature. ►Thermal energy transfer is heat moving from a warmer object to a cooler object.  How is Heat Transferred? There are THREE ways heat can move. – Conduction – Convection – Radiation  CONDUCTION ►Heat is transferred from one particle of matter to another in an object. ► Conduction = CONTACT Conduction When you heat a metal strip at one end, the heat travels to the other end. As you heat the metal, the particles vibrate, these vibrations make the adjacent particles vibrate, and so on and so on, the vibrations are passed along the metal and so is the heat. We call this? Conduction Metals are different The outer e______ lectrons of metal atoms drift, and are free to move. When the metal is heated, this ‘sea of inetic electrons’ gain k_____ energy and transfer it throughout the metal. Insulators, such as w___ ood and p____, lastic do not have this ‘sea of electrons’ which is why they do not conduct heat as well as metals. Why does metal feel colder than wood, if they are both at the same temperature? Why does metal feel colder than wood, if they are both at the same temperature? Metal is a conductor, wood is an insulator. Metal conducts the heat away from your hands. Wood does not conduct the heat away from your hands as well as the metal, so the wood feels warmer than the metal.  Have you ever… ► Touched a metal spoon sitting in a pan of boiling water only to be surprised by HOW hot it is? What conducts heat better, metal or nonmetal? Why? EXAMPLE OF CONDUCTION ►A piece of cheese melts as heat is transferred from the meat to the cheese (Contact) CONVECTION ► Convection is the movement that transfers heat within fluids ► Fluids = anything that flows ► Heat is transferred by currents within the fluid or gas Convection What happens to the particles in a liquid or a gas when you heat them? The particles spread out and become less dense. What is a fluid? A liquid or gas. This effects fluid movement. Fluid movement Cooler, more d____, ense fluids sink through w_____, armer less dense fluids. In effect, warmer liquids and gases r___ ise up. Cooler liquids and gases s___. ink Water movement Cools at the Convection surface current Cooler Hot water water sinks rises Cold air sinks Where is the Freezer freezer compartment compartment put in a fridge? It is warmer at the It is put at the bottom, so top, because this warmer cool air sinks, air rises and so it cools the a convection food on the current is way down. set up. Examples of Convection: ►Have you ever noticed that the air on the second floor of your house is warmer than the first floor? Or that water in a pool is cooler at the deep end? Convection questions Why does hot air rise and cold air sink? Cool air is more dense than warm air, so the cool air ‘falls through’ the warm air. The third method of heat transfer How does heat energy get from the Sun to the Earth? There are no particles between the Sun and the Earth so it CANNOT travel by conduction or by convection. RADIATION ? RADIATION ► Radiation is the transfer of energy by waves ►What type of waves? ►ELECTROMAGNETIC ► Radiation does NOT require matter to transfer thermal energy Radiation Radiation travels in straight lines True/False Radiation can travel through a vacuum True/False Radiation requires particles to travel True/False Radiation travels at the speed of light True/False Radiation May Come From Other Sources Have you ever sat too close to a campfire? You’re enjoying the warmth ….. only to notice that your skin is really warm? Examples of RADIATION 1. Fire 2. Heat Lamps 3. Sun BLACK BODY Emission experiment Four containers were filled with warm water. Which container would have the warmest water after ten minutes? Dull metal Shiny black Shiny metal Dull black shiny metal container would be the warmest after ten The __________ radiation back minutes because its shiny surface reflects heat _______ dull black container into the container so less is lost. The ________ emitting heat would be the coolest because it is the best at _______ radiation. Absorption experiment Four containers were placed equidistant from a heater. Which container would have the warmest water after ten minutes? Dull metal Shiny black Shiny metal Dull black dull black container would be the warmest after ten The __________ minutes because its surface absorbs heat radiation _______ the best. shiny metal container would be the coolest because it is The _________ the poorest at __________ absorbing heat radiation. Radiation questions Why are houses painted white in hot countries? Why are shiny foil blankets wrapped around marathon runners at the end of a race? Radiation questions Why are houses painted white in hot countries? White reflects heat radiation and keeps the house cooler. Why are shiny foil blankets wrapped around marathon runners at the end of a race? The shiny metal reflects the heat radiation from the runner back in, this stops the runner getting cold. QUIZ #4 1. Which of the following is not a method of heat transfer? A. Radiation B. Insulation C. Conduction D. Convection 2. In which of the following are the particles closest together? A. Solid B. Liquid C. Gas D. Fluid 3. How does heat energy reach the Earth from the Sun? A. Radiation B. Conduction C. Convection D. Insulation 4. Which is the best surface for reflecting heat radiation? A. Shiny white B. Dull white C. Shiny black D. Dull black 5. Which is the best surface for absorbing heat radiation? A. Shiny white B. Dull white C. Shiny black D. Dull black 6. Heat transfer by convection occurs when; A. electromagnetic waves travel from one place to another through a vacuum. B. electrons bump into other electrons. C. atoms give off heat in the form of electromagnetic waves. D. particles of a fluid move from place to place. E. none of the above 7. The reason you can hold your fingers beside (but not above) a candle flame without getting hurt is that A.hot air rises. B. air is a poor heat conductor. C. hot-air convection currents travel upward. D. all of the above 8. Heat travels from the sun to Earth by A.conduction. B. radiation C. convection D. insulation E. vacuumization 9. Energy transfer by convection is primarily restricted to A.gases. B. liquids. C. solids. D. Liquids and gases. E. Solids, liquids, and gases. 10. Rising warm air currents is an example of A. Radiation B. Conduction C. Convection D. Condensation