The heat capacity of a substance is a measure of how well the substance stores heat. Whenever we supply heat to a material, it will necessarily cause an increase in the material's temperature. The heat capacity is defined as the amount of heat required per unit increase in temperature, so that
Thus, materials with large heat capacities, like water, hold heat well -
their temperature won't rise much for a given amount of heat - whereas
materials with small heat capacities, like copper, don't hold heat well -
their temperature will rise significantly when heat is added.
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