2 S8P2 d. Describe how heat can be transferred through matter by collisions of atoms (conduction) or through space (radiation). In a liquid or gas, currents will facilitate the transfer of heat (convection).
3 BackgroundAll forms of matter, whether solid, liquid, or gas, are composed of atoms or molecules in constant motionBecause of this constant motion, all atoms have thermal (heat) energyWhenever a substance is heated, the atoms move faster and fasterWhen a substance is cooled, the atoms move slower and slowerThe “average motion” of the atoms that we sense is what we call temperatureTemperature and heat ARE NOT technically the same thingTemperature is the average motion of atoms and molecules; heat is the energy that flows due to temperature differences
4 Lesson Essential Question: How is energy transferred as heat?
5 How is energy transferred as heat? Activating Strategy:Activating AcrosticFor each of the letters of the phrase on the following slide write one word that would characterize the phrase.
7 The transfer of energy between the particles of two objects due to a temperature difference between the two objects is called heat.
8 The transfer of energy always takes place from a substance at a higher temperature to a substance at a lower temperatureTemperature is an indicator of the particles’ average kinetic energy; therefore, you can use it to predict which way energy will be transferredThe greater the difference in the temperatures of two objects, the more energy that will transfer as heat
9 Energy can be transferred as heat in three ways: ConductionConvectionRadiation
11 ConductionConduction is the transfer of energy that occurs when molecules bump into one another (heat transfer from one atom to another within a substance).
12 Solid at Different Temperatures ConductionMolecules are always in motion, but molecules in warmer objects move faster than molecules in cooler objects.Solid at Different Temperatures
13 ConductionWhen objects are in contact, energy is transferred from warmer objects to cooler objects.
14 ConductionExample of conduction: A spoon in a cup of hot soup becomes warmer because the heat from the soup is conducted along the spoonConduction is most effective in solids, but it can happen in fluids. Gases and liquids are generally poor conductors of heat because their molecules are farther apart than are the molecules in solids. Therefore, neighboring molecules in a gas or in a liquid are less affected by the increased motions of heated molecules, and consequently heat is not conducted rapidly.
15 ConductionUse the following website to view animations of energy transfer by conduction in solids, liquids, and gases.
16 ConductionWhy does the lady in the pink dress drop her roasting stick when the lady in the blue dress does not?
17 When heat is conducted, it is led from the heat source by traveling along a physical object. The young woman in the pink dress was using a straightened out coat hanger wire to cook her marshmallow. Metal is a good conductor of heat. The heat from the fire traveled along the thick metal wire. The wire got so hot that the girl had to let go of it. The young girl in the blue dress is using a wooden rod to hold her marshmallow. Wood does not conduct heat well. The wood in her hand is still cool and the marshmallows are almost done!
18 ConductionAny material through which energy can be easily transferred as heat is called a conductorWhat determines how well a substance conducts is whether it is a gas, liquid, or solidGases are extremely poor conductors because their particles are far apartLiquids conduct better than gases, but they are still not very effective conductorsSome solids, like rubber and wood, conduct energy about as well as liquidsMetals such as copper and silver conduct heat transfer very wellSome solids conduct better than othersIn general, metals are better conductors than nonmetals
19 ConductionA material that is a poor conductor that is used to reduce or stop energy is called an insulatorEx. Wood
22 ConvectionConvection is the transfer of heat by the flow of material. Convection circulates heat.
23 Convection Heat moves with the fluid Warmer portions are less dense and therefore rise; cooler portions fall because they are denser. When the atoms at the top cool down, they become more dense and fall and vice versa for the warmer atoms. Hence a continuous cycleThe cycle of a heated fluid that rises and then cools and falls is called a convection current
28 RadiationRadiation is energy that is transferred in the form of rays or electromagnetic waves. This includes infrared radiation, visible light, and ultraviolet rays.
29 Radiation What happens in space? There are no solids touching the sun for conduction to occurThere are no fluids in space for convection to occurTherefore, heat travels by radiation
30 Use the animations on the website below to review conduction, convection, and radiation: Scroll down until you see the stove
31 Think, Pair, Ink Look at the diagram below Think, Pair, Ink Look at the diagram below. In a sentence or two explain how radiation, conduction, and convection are used or prevented.
32 The shiny inside reflects radiant energy back into the fluid The shiny inside reflects radiant energy back into the fluid. It also prevents heat from entering the thermos from outside. The vacuum space prevents conduction and convection from occurring. Since heat cannot easily leave or enter the thermos, fluids retain their original temperature.
33 Conduction, Convection, and Radiation together distribute the Sun’s heat throughout the Earth
34 Lesson Essential Question: How is energy transferred as heat? Summarizing Strategy:On the following slides, identify whether the statement describes cooking popcorn using conduction, convection, or radiation.
35 Put oil in the bottom of a pan Put oil in the bottom of a pan. Cover the bottom of the pan with popcorn kernels. Place the pan on the stove and turn on the burner to medium heat. Cover the pan with a lid. Periodically shake the pan so the kernels move around in the oil.
36 And the answer is… Conduction The heat is transferred by direct contact from the pan, to the oil, to the kernels of popcorn.