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Why polished surfaces are colder?

  1. Aug 23, 2010 #1
    Why of two floors made of the same material, the polished one is (at least feels) colder than the rough one.

    Just compare two concrete floors, one polished and one unpolished.

    Thanks
     
  2. jcsd
  3. Aug 23, 2010 #2
    I would think its just that it feels colder because maybe the polished one has higher heat conductivity, so your feet loses heat more quickly. Thats just my thought.
     
  4. Aug 23, 2010 #3

    Borek

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    Staff: Mentor

    My bet is Sakha is close, but not there yet. Think about contact surface between your feet and the surface. When is it larger - for the polished, or rough surface? How does the heat flow depend on the contact surface?
     
  5. Aug 23, 2010 #4
    It is due to an effect called thermal contact.

    Imagine that you were looking at the interface, the surface between your skin and the floor, with a microscope.
    The smooth surfaces would be in close contact and heat would conduct across easily. If the floor were warm it would feel warm, and cold if it were colder than your skin.
    But a rough surface would make contact only in spots where the high points met your skin. Very little heat would pass in either direction because it would have to jump the air gap between the high points.
    If you pressed harder, it would make no difference when smooth surfaces were in already in good thermal contact, but it would make the rough floor feel colder because some of the high points would be squashed down, increasing the amount of contact between the surfaces.
    Or you could spill a little water under your feet to fill the air-gap. Water conducts heat better than the air, and gives a better thermal contact.
     
  6. Aug 23, 2010 #5
    Thanks. That makes sense.
     
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