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Heat and Thermodynamics. 16.2. Conduction. The transfer of thermal energy with no overall transfer of matter . Conduction occurs within a material or between materials that are touching . This device, called Newton's cradle, helps to visualize conduction.
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Conduction • The transfer of thermal energy with no overall transfer of matter. • Conduction occurs within a material or between materials that are touching. This device, called Newton's cradle, helps to visualize conduction. After one ball strikes the rest, most of the kinetic energy is transferred to one ball on the end.
Conduction • Conduction in gases is slower than in liquids and solids because the particles in a gas collide less often • In most solids, conduction occurs as particles vibrate in place and push on each other. • In metals, conduction is faster because some electrons are free to move about.
Thermal Conductor • Amaterial that conducts thermal energy well. • Example 1: A wire rack in a hot oven can burn you because the metal conducts thermal energy so quickly. • Example 2: Pots and pans often are made of copper or aluminum because these are good conductors.
A thermal conductor doesn't have to be hot! • Why does a tile floor feel colder than a wooden floor? • Both floors are at room temperature. • But the tile feels colder because it is a better conductor and transfers thermal energy rapidly away from your skin.
Thermal Insulator • A material that conducts thermal energy poorly • Example 1: • Wood • heats up slowly because it is a poor conductor of thermal energy; therefore a goodinsulator • Example 2: • Air • Found in between panes of a double-paned window • Insulate house in winter/keep heat out in summer • Examples 3/4: • Wool and foam cups • Both use trapped air to SLOW DOWN conduction
Convection • The transfer of thermal energy when particles of a fluid move from one place to another. • The moving sandbags are like the particles in a fluid. The wall grows taller as more and more sandbags arrive. • In much the same way, particles in a fluid can transfer thermal energy from a hot area to a cold area.
Convection Currents • Hot Cold • Occurs when a fluid circulates in a loop as it alternately heats up and cools down. • Example 1: Air circulating in an oven or room • “Hot air rises” less dense than cold air • Example 2: important in many natural cycles • ocean currents • weather systems • movements of hot rock in Earth's interior
Radiation • The transfer of energy by waves moving through space. • Example 1: Heat lamps used in restaurants • Example 2: Sun warms you • All objects radiate energy. As an object's temperature increases, the rate at which it radiates energy increases
Radiation Example 3: • A heating coil on a stove radiates thermal energy. • The changing color of the red arrows indicates that the farther you are from the coil, the less radiation you receive.
