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Homework Help: Why is the equation for heat flow negative?

  1. May 18, 2017 #1
    1. The problem statement, all variables and given/known data
    q = -kdp/dx

    2. Relevant equations

    q = heat flow
    k = constant
    p = thermal energy density
    3. The attempt at a solution
    This equation says that when heat flows from hot to cold the thermal energy density increases but why? I thought heat meant a higher thermal energy density and hot to cold meant a lower energy density since the molecules that make up the air are slower when cold.
  2. jcsd
  3. May 18, 2017 #2
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