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Specific Heat CapacityThermal Energy Needed To Change an Object's TemperatureThe heat energy needed to change the temperature of an object depends on the heat capacity of the object. The specific heat is the heat capacity divided by the mass.
The amount of energy needed to raise the temperature of an object depends on both the mass and composition of the object. The heat capacity measures the combined effect of mass and composition. The specific heat, or specific heat capacity, is a property of the composition only. Total Heat CapacityAn object's total heat capacity, often called heat capacity, is the amount of thermal energy required to raise its temperature by one centigrade degree. Heat capacity is usually measured in units of joules per centigrade degree. It is however possible to use other energy units, such as calories or BTUs, or Fahrenheit instead of centigrade degrees. For example, an object might have a heat capacity of 150 joules per centigrade degree. Adding 150 joules of thermal energy will raise its temperature by 1 centigrade degree. Adding 300 joules will raise the temperature 2 centigrade degrees, etc. If thermal energy is removed from the object rather than added to it the temperature will drop the same number of degrees. The heat capacity of an object is determined by both its composition and mass. For example, when eating hot soup the small amount of soup in a spoon will cool faster than the larger amount of soup in the bowl. Both the spoonful and the bowlful have the same composition, but the spoonful has a lower heat capacity. (Other factors such as the ratio of surface area to volume can also affect how fast something cools.) To remove the effect of the mass, scientists divide the total heat capacity by the mass to get the specific heat. Specific HeatThe specific heat, sometimes called the specific heat capacity, is a property of the type of material only. Dividing the heat capacity by the mass causes the mass or amount of material to cancel out. If the soup is uniform, without large clumps of various ingredients, the bowl of soup and the spoonful of soup both have the same specific heat, but the bowlful has a larger heat capacity. Heat capacity applies to specific objects. Specific heat applies to a type of material. Specific heat is usually measured in units of joules per centigrade degree per kilogram. As for heat capacity, it is possible to use other energy units or Fahrenheit degrees. It is also possible to use other mass units, such as grams. Scientists use tables of specific heats of various types of materials. The specific heats are measured experimentally. For gasses the heat capacity and the specific heat depends on the process by which the temperature changes. In particular the temperature can change in a way that keeps the pressure constant or in a way that keeps the volume constant. So physicists must specify if the specific heat is at a constant pressure or at a constant volume. The temperature of an object is a measure of its random molecular motions. It increases as the average speed of the atoms or molecules increases. Different types of materials have different specific heats because various types of molecules and atoms require different amounts of energy to increase their speed. For the same type of material, a more massive object will have a larger heat capacity because it has more molecules that must move faster to increase the temperature. Therefore they need more thermal energy to raise the temperature. The heat capacity and specific heat apply to changing an object's temperature only if it remains in the same state: solid, liquid, or gas. Physicists use latent heats to find how much energy is required for something to change from one state to another. Further ReadingWilson, J.D., Buffa, A.J., and Lou, B., College Physics 6th ed., Pearson, 2007.
The copyright of the article Specific Heat Capacity in Physics is owned by Paul A. Heckert. Permission to republish Specific Heat Capacity in print or online must be granted by the author in writing.
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