Understanding Heat Transfer, Conduction, Convection and Radiation
Understanding Heat Transfer, Conduction, Convection and Radiation 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.
Question If a cup of coffee and a red popsickle 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 popsickle will melt and then the liquid will warm to room temperature. Heat Transfer Methods Heat transfers in three ways: Conduction
Convection Radiation 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______ lectronsof metal atoms drift, and are free to move. When the metal is heated, this sea of electrons gaininetic k_____ energy and transfer it throughout the metal. Insulators, such as ood
w___ andlastic p____, 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? 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. Convection What happens to the particles in a liquid or a gas when you heat them? The particles spread out and become less dense. This effects What A liquid is
fluid a orfluid? gas. movement. Fluid movement Cooler, more ense d____, fluids sink through armer w_____, less dense fluids.
In effect, warmer liquids and gases r___ ise up. Cooler liquids and gases ink s___. Water movement Cools at the surface Cooler water sinks
Convection current Hot water rises Why is it windy at the seaside? Cold air sinks Where is the freezer
compartment put in a fridge? It is put at the top, because cool air sinks, so it cools the food on the way down. Freezer compartmen
t It is warmer at the bottom, so this warmer air rises and a convection current is set up. 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 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 Emission experiment
Four containers were filled with warm water. Which container would have the warmest water after ten minutes? Dull metal Shiny metal Shiny black 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 metal Shiny black Dull black dull black container would be the warmest after ten The __________ radiation the best. minutes because its surface absorbs heat _______ shiny metal container would be the coolest because it is
The _________ the poorest at __________ absorbing heat radiation. 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. Why are boilers placed beneath hot water tanks in peoples homes? Hot water rises. So when the boiler heats the water, and the hot water
rises, the water tank is filled with hot water. 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. 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
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