Specific heat is basically a measurement of how hot something becomes when heat is applied to it. The same amount of heat makes a given amount of iron hotter than a given amount of water.
To determine the specific heat of a material, we need a material in pure form. We cannot determine the specific heat of iron if we use iron mixed with an unknown amount of other materials.
We also need a unit to show the mass of the material being heated. The mass of an object is the amount of matter it possesses. “Serway’s College Physics” defines mass as “a measure of the object’s resistance to changes in its motion” when a force is applied to it. This definition is appropriate. The more matter an object contains, the harder it is to speed it up or to slow it down. When Sandy Koufax threw a fastball in a Brooklyn Dodgers baseball game, it was easy for Roy Campanella to catch it. However, if a cannonball had been traveling toward him at the same speed, he would not even have tried to stop it.
In our physics class long ago, we used the convenient gram as the mass unit for specific heat measurements. The newer International System of Units, abbreviated SI, prefers to use the kilogram.
We also need a unit to show how much heat is applied to the object under consideration. Our physics class used the calorie. When one calorie of heat is applied to one gram of water, its temperature becomes one Celsius degree warmer than it was before. “Serway’s College Physics” defines the calorie as “the energy necessary to raise the temperature of 1 g of water from 14.5˚ to 15.5˚ C.”
The International System of Units uses the joule. The joule is smaller than the calorie. You have to expend 4.186 joules of energy before you generate one single calorie.
Note that the calories discussed above are not the same as the calories that you eat. The dietary calorie is equal to 1,000 of the calories that the physicist likes to use.
In both cases discussed above, the Celsius scale was used to measure temperature. The Fahrenheit scale has also been used. In this case, the heat energy applied is measured in British thermal units and the mass of the object is measured in pounds.
The system we used for specific heat measurements was very convenient. The specific heat of a given material was defined as the amount of heat energy that you had to apply to one gram of the material under consideration in order to raise its temperature one degree centigrade, or Celsius. From the definition of the calorie, we know that one calorie will make one gram of water hotter by one degree Celsius. So the specific heat of water is one calorie per gram per degree Celsius.
Water has a higher specific heat than other substances. In comparison, you need 0.03 calories to raise one gram of gold one degree Celsius. The corresponding figure for iron is 0.11, while the specific heat of aluminum is 0.215 calories per gram per degree Celsius.
Using SI units, the specific heat will be 4186 times greater than the figures given above. For example, the specific heat of water will be 4186 joules per kilogram per degree Celsius. (I am following “Serway’s College Physics” in applying the Celsius scale to computations of specific heat. I believe that the SI unit for temperature is actually the kelvin. However, the results will be the same in either case, since a Kelvin degree has exactly the same size as a Celsius degree.
There are tables that give the specific heat of such materials as air, wood, and granite. When using such figures, it is necessary to remember that these materials are mixtures with variable composition. For example, some wood may contain more water than wood that has been dried more thoroughly. In such a case, the former would have a higher specific heat.
Air, or even a homogeneous gaseous substance, such as nitrogen or oxygen, presents special problems. In measuring the specific heat of gases, either the pressure or the volume must remain constant, and the procedure used will affect the results.
I shall conclude this presentation with a formula given in “Serway’s College Physics:”
Q = mcΔt. Q is the amount of heat applied to an object; m is the mass of the object; c is the specific heat; Δt is the change in temperature of the object.
References
“Serway’s College Physics” by Jerry S. Faughn, Raymond A. Serway, Chris Vuille, and Charles A. Bennett
“Barron’s E-Z Physics” by Robert L. Lehrman