When heat flows from one material to another, the temperature of the contact layer of the cooler material increases.  From the contact layer thermal energy has to spread throughout the cooler material by conduction or convection.  How fast the temperature in the contact layer increases depends on the specific heat capacity of the material.  The specific heat capacity c is the amount of energy it takes to raise the temperature of one kg of material by 1 degree Kelvin or Celsius.

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Specific heat capacities: (kcal/(kgoC))

 Water 1 Ice 0.49 Steam 0.48 Glass 0.2 Steel 0.11 Copper 0.092 Aluminum 0.215

The unit kcal (kilocalorie) is a unit of energy.  1 kcal = 4186 J.  In units of kcal/(kgoC) the specific heat of water is 1.

The specific heat capacity of water is approximately 4 times higher than that of air.  The exact specific heat capacity of a substance depends on the condition under which it is measured.  For gases, the specific heat capacity measured at constant volume is different from the specific heat capacity measured at constant pressure.

The smaller the specific heat capacity of a material that touches your skin, the less heat it takes to bring the temperature of the boundary layer up to the temperature of your skin.  How fast the heat is carried away from this boundary layer now depends on the thermal conductivity of the material and on whether or not convection currents are present.  To minimize heat loss from your skin, surround it by material of low specific heat capacity and low conductivity, and prevent convection.  In addition you must minimize heat loss via radiation.

#### Problem:

A 50g sample of copper is at 25 oC.  If 1200 J of thermal energy is added to it, what is the final temperature of the copper?

• Solution:
ΔT = ΔQ/(cm).  For copper c = 9.2*10-2 kcal/(kgoC).
ΔT = 1200 J*(1 kcal/4186 J)/(0.05 kg*9.2*10-2 kcal/(kgoC)) = 62.3 oC.
T = 87.3 oC.