Heat Transfer Conduction, Convection, and Radiation Heat • Heat is thermal energy moving from one object at one temperature to an object at a different temperature. 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 without the movement of the object. • Conduction=CONTACT Have you ever… • Touched a metal spoon sitting in a pan of boiling water only to be surprised by hot HOW it is?? Example of Conduction • Think of a metal spoon in a pot of hot water being heated on an electric stove. • The fast-moving particles of the hot electric coil (in the stove) collide with the slow-moving particles of the cool pot. • Because of these collisions, the slower particles move faster and heat is transferred. • Then the particles of the pot collide with the particles in the water, which collide with the particles at one end of the spoon. • As the particles move faster, the metal spoon gets hotter. This process of conduction is repeated all along the metal until the entire spoon is hot. Examples of Conduction • A piece of metal in a forge glows red as heat is transferred to the metal from the forge. 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. CONVECTION • Convection is the movement that transfers heat within the water. • In convection, heat is transferred by the movement of currents within a FLUID (liquid OR gas) • Convection=VENTS through air and liquid particles Have you ever… • noticed that the air near the ceiling is warmer than the air near the floor? RADIATION • Radiation is the transfer of energy by electromagnetic waves. • Radiation does NOT require matter to transfer thermal energy. (Passes through a vacuum.) • Radiation=RADIATES (heat escaping the sun) Have you ever… • sat too close to a campfire while cooking marshmallows– enjoying the warmth-- only to notice (when you move) that your skin is really warm? Example of RADIATION • You can FEEL the radiation from a bonfire from several meters away! Examples of Radiation • Think of the sun’s radiation…it travels through MILLIONS of kilometers of empty space to reach us. • Radiation from heat lamps • A blacksmith feels radiation from his forge. 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.
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