Ch. 5 - Energy II. Thermal Energy (p.134-137, 141-144) Temperature Thermal Energy Heat Transfer.
Ch 13: Heat and Temperature
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Transcript of Ch 13: Heat and Temperature
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Ch 13: Heat and Temperature
• Temperature–measure of the average KE
(motion) of particles (atoms or molecules)–Faster they move…more KE…
higher temperature–Higher temperature…faster they
move…more KE
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Thermometers• Thermometers work because the substance
(alcohol if it’s red, mercury if it’s silver) heats up, expands and rises
• 3 temperature scalesoC oF K
• water freezes 0o 32o 273• water boils 100o 212o 373• room temp 22o 72o 295• body temp 37o 98o 310• lowest temp -273o -460o 0
• Kelvin scale is an absolute scale… nothing can go lower than 0K (absolute zero), because at 0K it has no energy…even atoms are frozen
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Temperature and Energy Transfer
• Things feel hot or cold because energy is being transferred
• This transfer of energy is called heat. Amount of heat transferred depends on temp. differences.
• Energy flows from high to low concentration, that is from hot to cold things
• Why does ice feel cold?
• Why does a heater feel hot?
• Because heat is leaving your hand
• Because heat is entering your hand
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Conduction and Convection
• when objects are in contact with each other, heat flows directly from the hotter one to the colder one. This is conduction.
• fluids (gas or liquid) move and take energy from hotter to colder. This is convection.
• if happens in a cycle due to changing densities, it is called a convection current.
• Both of these only happen when there is matter present (not in a vacuum, like space)
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Radiation
• Energy transferred without contact, by electromagnetic waves
(visible light, UV, infrared, microwaves, etc.)
• Only form of heat transfer that does not need matter to happen, but
can happen with matter, too.
• Movie: Comparing Convection, Conduction, and Radiation
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Where do you see all three?
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Conductors and Insulators• Materials that carry/transfer heat
energy well are called conductors. Most metal objects are good conductors.
• Materials that do not allow heat energy to flow are called insulators. Styrofoam, gasses, wood, plastic and rubber are all good insulators.
• So how does styrofoam keep something both hot and cold?
• It doesn’t “know”…it just doesn’t allow heat to transfer either way…in or out.
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