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The information below is intended to provide introductory material for elementary students and further material for high school students.

Please keep in mind that not all demonstrations are presented at each show, and each topic may not be covered.


THERMAL CONDUCTIVITY

Introduction

  • Heat moves through a material at a specific rate. The rate it travels depends on the material itself: some materials allow heat to move quickly through them, some materials allow heat to move very slowly through them.

    When heat is applied to a portion of a material, that heat will move through the material. Depending on the composition of the atoms of that material, the heat may move very slowly, or it may move very quickly. Heat moves very quickly through a metal spoon, for instance: leaving one end of a spoon in boiling water will make the entire spoon hot very quickly. The entire spoon becomes hot, not just the spot in the boiling water. On the other hand, heat moves very slowly through the insulation in your house. When it is very cold outside, the heat from your house moves slowly from one side of the insulation to the other. This helps keep the heating costs of your house down.


  • When two objects of different temperatures are put in contact with one another, there is an exchange of thermal energy. This exchange, known as heat conduction, causes the warmer object to cool and the cooler object to warm.


  • The thermal energy of an object is a measure of the speed of the object's particles. When two objects of different temperatures are put in contact with one another, the faster moving particles collide with the slower moving particles, and energy is exchanged. The faster moving particles give up some energy and therefore slow down and the slower moving particles gain some energy and therefore speed up. This process, known as heat conduction, continues until an equilibrium is reached, where all the particles of both objects are moving at roughly the same speed. This equilibrium speed (or equilibrium temperature) must be somewhere in between the two objects' original temperatures. Therefore, the warmer object cools and the cooler object warms.

    More Specifically

  • The thermal current is directly proportional to the coefficient of thermal conductivity. Different materials have different coefficients of thermal conductivity.

    When heat is applied to a portion of a material, that heat will move through the material. This movement of heat through a material is called the thermal current. Depending on the composition of the atoms of that material, the heat may move very slowly, or it may move very quickly. This dependance is quantified by the coefficient of thermal conductivity. Each material has a unique coefficient of thermal conductivity. A high coefficient means heat moves very quickly; a low coefficient means heat moves very slowly. Below is a chart of thermal conductivities for some common materials. Compare your own empirical knowledge of how quickly heat moves through these materials with the values in the chart.

  • Material Coefficient of Thermal Conductivity (W/mK)
    Air 0.026
    Water 0.609
    Glass 0.8
    Concrete 1.0
    Steel 46
    Copper 401
    Values taken from Tipler, Paul A. Physics, Third Edition. 1991.


  • When two objects of different temperatures are put in contact with one another, there is an exchange of thermal energy. This exchange, known as heat conduction, causes the warmer object to cool and the cooler object to warm.


  • The thermal energy of an object is a measure of the speed of the object's particles. When two objects of different temperatures are put in contact with one another, the faster moving particles collide with the slower moving particles, and energy is exchanged. The faster moving particles give up some energy and therefore slow down and the slower moving particles gain some energy and therefore speed up. This process, known as heat conduction, continues until an equilibrium is reached, where all the particles of both objects are moving at roughly the same speed. This equilibrium speed (or equilibrium temperature) must be somewhere in between the two objects' original temperatures. Therefore, the warmer object cools and the cooler object warms.

    Related Demos

    The following demonstrations illustrate this physics topic:

    Sponsored by the Physics Department and the Center for Science, Mathematics, and Engineering Education -- University of Virginia