2 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.
3 QuestionIf a cup of coffee and an ice cube were left on the table in this room what would happen to them? Why?AnswerThe cup of coffee will cool until it reaches room temperature. The ice will melt and then the liquid will cool to room temperature.
4 HEAT TRANSFER METHODSConductionConvectionRadiation
5 CONDUCTIONHeat travels along a substance from molecule to molecule (between two materials that touch each other)Good conductors (silver, copper, gold)Poor conductors ( glass, paper, Styrofoam)
6 ConductionWhen 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?
7 Metals are differentThe outer e_______ for metal atoms drift, and are free to move.lectronsWhen the metal is heated, this ‘Sea of electrons’ gain k_____ energy and transfer it throughout the metal.ineticInsulators, such as w___ and p____, do not have this ‘Sea of electrons’ which is why they do not conduct heat as well as metals.oodlastic
8 Why does metal feel colder than wood, if they are both at the same temperature? Metal is a conductor, wood is an insulator. The metal conducts the heat away from your hands, the wood does not conduct the heat away from your hands as well as the metal, so the wood feels warmer than the metal.
9 CONDUCTION EXAMPLES water heating on an electric stove hot sand touching your feettouching a stove and being burnedice cooling down your handboiling water by thrusting a red-hot piece of iron into it
10 CONVECTION transfer of energy as it is carried through a liquid or gas heat transfer by a circulation of rising warm air (less dense) and sinking cooler air (denser).“Hot air rises” the more dense air sinks forcing the less dense air upward
11 The particles spread out and become less dense. Heating fluidsWhat 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.
12 Fluid movementCooler, more d____, fluids sink through w_____, less dense fluids.ensearmerIn effect warmer liquids and gases r___ up.iseCooler liquids and gases s___.ink
13 Water movement Cools at the surface Convection current Hot water rises Cooler water sinks
15 Where is the freezer compartment put in a fridge? Cold air sinksWhere is the freezer compartment put in a fridge?Freezer compartmentIt is warmer at the bottom, so this warmer air rises and a convection current is set up.It is put at the top, because cool air sinks, so it cools the food on the way down.
16 CONVECTION EXAMPLESmacaroni rising and falling in a pot of heated waterheat rising from a chimneyan old-fashioned radiator (creates a convection cell in a room by emitting warm air at the top and drawing in cool air at the bottom)
17 RADIATIONCarries energy away from the hot object and causes it to cool downThe movement of heat in a wave-like motion through an empty space
18 ? RADIATION 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?
19 Radiation travels in straight lines True/False Radiation requires particles to travelRadiation travels at the speed of light
20 RADIATION EXAMPLES sunlight heat from toaster heat from a light bulb heat from a fireheat from anything else which is warmer than its surroundings
21 hot water rises and cold water sinks CONVECTION
41 ANSWER KEY hot water rises and cold water sinks - Convection stir frying vegetables - Conductiona spoon in a cup of hot soup becomes warmer - Conductiongrilling hamburgers over a charcoal flame - Radiationhot air balloon rises - Convectionyou feel the heat from a campfire - Radiationa raw egg begins to fry as it hits a heated frying pan - ConductionHeated air rises, cools, then falls. Air near heater is replaced by cooler air, and the cycle repeats. - Convectionboiling potatoes in water –Conduction (water to potato)microwave oven - Radiationpropane heater - Radiationbasement is cooler than attic - Convectionradiator warms your hands - Convectiona person takes a warm bath - Conductionheat from a light bulb - Radiationhot pan is cooled by running it under cold water - Conductionyou get sunburned - Radiationwarm water at the surface of the swimming pool - ConvectionIroning a shirt - Conductionwind currents - Convection