When something rises in temperature, we say it has gotten hotter. It seems pretty straightforward. A higher temperature means more heat, so heat and temperature are the same thing, right? It’s not quite as simple as that. Yes, heat and temperature are strongly related, but they are not the same thing. In fact, as we will see, a higher temperature does not always mean more heat.
What Is Heat?
Heat is a form of energy. It is created by the vibration of the atoms and molecules that make up an object. The faster these particles move, the more heat they create. Even when something is extremely cold, the atoms and molecules within it are moving, and that object does contain some heat energy.
When two objects come in contact with each other, heat will be transferred from the hotter object to the cooler one, until the objects are the same temperature. When cold water is added to hot water, for example, heat from the molecules of hot water is transferred to the molecules of cold water, until all the water molecules are the same temperature.
Common sense suggests that the way to make something hotter is to add heat to it. Although this does work, adding heat is not the only way to make something hotter. A microwave oven, for example, does not cook food by generating heat. Instead, the microwaves penetrate the food and make the molecules within the food vibrate at a faster rate. As a result, the food gets hot, even though no heat has been transferred into it.
Some chemical reactions generate heat, as well. Skiers, hunters, and others who spend time outside during cold weather often use hand warmers, which are small packets that generate heat when they are opened. Clearly, no heat has been added to these packets. In fact, the air they have been exposed to is quite cold. They become warm because exposure to air triggers a chemical reaction which creates heat.
What Is Temperature?
Because heat is generated by vibrating molecules, objects containing more molecules contain more heat. A bathtub full of hot water contains more heat than a glass of hot water. Yet, when we dip a finger into each of them, the sensation of warmth on our finger may be the same. How can this be, if the tub of water contains so much more heat? This is where temperature comes in.
Temperature is a measurement of heat. It tells us the average amount of heat contained in the molecules of an object. If the average amount of heat contained in a single molecule of water in the glass is the same as that of a single molecule of water in the tub, then these bodies of water have the same temperature.
Because it is an average, temperature is independent of the number of molecules in an object, unlike heat, which increases as the number of molecules of an object increases. This is why a glass of water and a tub of water can have the same temperature even though they contain vastly different amounts of heat.
Think of it this way: A tub of hot water can raise the temperature of the room it is in, while a glass of water at the same temperature cannot. This is because the tub of water contains so much more heat than the glass of water.
A Final Example
Here’s an extreme example to illustrate the point. According to Encyclopedia Britannica , an iceberg contains more total heat than a burning match, even though the temperature of the match is much higher. Although each molecule of the iceberg contains only a small amount of heat, there are a huge number of them. The sum of all the tiny amounts of heat within the iceberg is greater than the sum of heat contained in the relatively small number of molecules in the flame of the match. There may be no better example of the difference between heat and temperature.
 Encyclopædia Britannica Online, “temperature.” http://www.britannica.com/EBchecked/topic/586581/temperature