8th Grade Chapter 5 Lesson 2


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  • 8th Grade Chapter 5 Lesson 2

    1. 1. Pgs. 186- 199 For Student Use Only 8 th Grade Chapter 5 Lesson 2
    2. 2. Heat Transfer <ul><li>Remember: Charles said that gases expand dramatically when heated </li></ul><ul><li>Liquids and Solids expand when heated also </li></ul><ul><ul><li>Have you ever experiences expansion in the real world? </li></ul></ul><ul><li>Example: </li></ul><ul><li>Expansion joints in bridges </li></ul>
    3. 3. <ul><li>Gas Expansion </li></ul><ul><ul><li>Gases expand because of loose cohesive bonds </li></ul></ul><ul><li>Liquid Expansion: </li></ul><ul><ul><li>Liquids expand also more than solids from lack of cohesive bonds </li></ul></ul><ul><li>Solid Expansion </li></ul><ul><ul><li>Solids expand differently due to stronger cohesion of molecules </li></ul></ul>Heat Transfer
    4. 4. Heat Transfer <ul><li>Expansion Joints </li></ul><ul><ul><ul><li>This allows bridge to expand and contract with temperatures </li></ul></ul></ul><ul><ul><ul><li>Concrete and Steel expand at nearly the same rate </li></ul></ul></ul><ul><li>Expansion of Water: </li></ul><ul><ul><li>Water molecules draw closer together as temperature drops </li></ul></ul><ul><ul><li>4 ° C is maximum density of water </li></ul></ul><ul><ul><li>O °C water begins to get larger and it freezes </li></ul></ul><ul><li>Water forms crystals that make the it larger and less dense (this is why ice floats). </li></ul>
    5. 5. Heat Transfer <ul><li>Thermostat </li></ul><ul><ul><li>Automatically regulates temperature </li></ul></ul><ul><ul><li>Uses Bimetallic strip to sense temperature changes </li></ul></ul><ul><ul><ul><li>Metals expand at different rates </li></ul></ul></ul><ul><ul><li>Cornelius Drebbel constructed the first thermostat </li></ul></ul>
    6. 6. Heat Transfer <ul><li>Heat flows from the hotter object to the colder object </li></ul><ul><li>Cold is merely a state of lower thermal energy </li></ul><ul><li>Heat flows in three different ways: </li></ul><ul><ul><li>Conduction </li></ul></ul><ul><ul><li>Convection </li></ul></ul><ul><ul><li>Radiation </li></ul></ul>
    7. 7. Heat Transfer <ul><li>Conduction: </li></ul><ul><li>Heat is transferred from one object to another </li></ul><ul><li>Think direct contact </li></ul><ul><li>Some materials are good conductors or some are not good conductors </li></ul><ul><li>Miner’s safety lamp disipates heat by conduction and keeps open flames from igniting methane gas </li></ul>
    8. 8. Heat Transfer <ul><li>Convection: </li></ul><ul><li>Heat is transferred through a fluid </li></ul><ul><li>Warmer fluids rise and colder fluids sink </li></ul><ul><li>This is known as convection currents </li></ul><ul><li>Convection currents are found in winds and waves and ovens </li></ul>
    9. 9. Heat Transfer <ul><li>Radiation: </li></ul><ul><li>Heat is transferred through space in the electromagnetic waves </li></ul><ul><li>This is a slower process and the glass stays close to the same temperature </li></ul><ul><li>Greenhouse Effect: </li></ul><ul><li>The atmosphere lets radiation in but traps heat </li></ul>
    10. 10. Heat Transfer <ul><li>Radiant Heat: </li></ul><ul><li>Radiation is absorbed and transferred much more readily from dark objects </li></ul><ul><li>Vacuum flask stores liquid oxygen, hydrogen, or other liquid gases. </li></ul><ul><li>Vacuum limits space conduction </li></ul><ul><li>Thermoses are a type of vacuum chamber </li></ul>
    11. 11. Heat Transfer <ul><li>Heat Transfer </li></ul><ul><ul><li>Heating homes uses a lot of different methods </li></ul></ul><ul><ul><li>Radiators- radiate heat </li></ul></ul><ul><ul><li>Conduction- is used to transfer the heat from the water to the metal bars </li></ul></ul><ul><ul><li>Convection – uses forced-air uses convection currents to help circulate the air. </li></ul></ul>