That there is a difference between heat and temperature is the kind of scientific fact that is often overlooked in casual conversation. "The temperature's really climbing" and "The heat is rising" are synonymous to most of us -- and yet the two statements are not the same. Understanding the nature of the difference is actually fairly simple, however.
Just because heat and temperature are not the same thing does not mean they are not closely related -- there is a reason for the fact that the concepts are often confused for one another.
A basic way to understand the difference and the relationship is through cause and effect -- changes in heat create changes in temperature. Adding heat generally raises temperatures, and removing heat generally lowers temperatures.
What Is Heat?
In a word, heat is energy. Specifically, it is the total kinetic energy contained by a substance. So to add heat to a substance is simply to add energy to it.
Adding heat to objects/substances can create two different effects on the recipients. As already mentioned, changes in heat create changes in temperature. The other effect of adding heat is that it can cause a change in state. This happens because additional heat can actually break the bonds between an object's molecules, which hold it in a given state.
Regarding the cause and effect relationship between of heat and temperature, it should be noted that a change in state actually does not involve a change in temperature. This, however, is something that we will have to return to once we have a fuller understanding of temperature.
What Is Temperature?
Temperature is a measurement of heat. It is not energy, but a number that represents the average kinetic energy of a substance's molecules. So whereas heat is actually every last bit of kinetic energy contained within a substance, temperature is a measure of the substance's average amount of kinetic energy.
As to why temperature does not change when a substance changes state, if we take the standard example of ice melting into water, we see that the temperature of the ice before melting is the same as that of the water immediately after melting. While heat/energy actually is absorbed in this change of state, it is applied to the breaking of the molecular bonds and not the temperature. Given enough added energy, temperature and state can both be affected, but for this to happen, the added energy must exceed the amount required solely to change the state.
The Classic Example
If all of this talk of molecules and kinetic energy isn't your cup of tea, perhaps the easier explanation lies in -- a cup of tea.
Consider the question: Which object contains more heat, a boiling hot cup of of tea or a massive iceberg?
The correct answer, as much as it goes against our instincts, is the iceberg. Though it is colder than the cup, its mass is considerably larger, thus giving it many more molecules. Since all molecules in matter move and thus have energy/heat, the total amount of heat is greater in the iceberg than in the cup of boiling tea. Put simply, greater mass means more energy.
The temperature, meanwhile, follows our instincts -- we know that boiling water has a higher temperature than ice, a fact that is true because temperature deals with averages and thus is not affected by mass.
To summarize, heat is the actual energy of an object/substance, while temperature is a measurement of the average energy of an object/substance. Thus the two concepts are inextricably linked and yet quite different.
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