What is Cold?

The Nation is in the grips of a weather event that has been described as frigid, cold, artic, etc. Essentially, most individuals would agree is the weather is cold. But does cold have a scientific meaning? Not, really, cold is a relative term. Similarly, hot is a relative term. People tend to think of hot or cold in terms of temperature. But, even temperature has a different scientific meaning than how we use it on a day-to-day basis.

How we use temperature daily is a measure of “hotness” and allows us a basis to compare the “hotness” of one object or location to another. Our understanding of “hotness” is comparative. We compare one item to another. Using this idea of comparisons, if I had two objects that have been heated in the oven, and I take one out and let it sit in the room for a bit while leaving the other in the oven, one would be “cold”, and one would be “hot.” It is relative.

Physicists use the idea of temperature to help us investigate heat. Heat is a form of energy. This is the field of thermodynamics. Absolute zero is the state where atoms are not moving, thus do not have kinetic energy (the energy due to motion), thus there is no heat. As we increase the energy, the atoms move, and we talk about raising the temperature. We are raising the energy, or heat. The concept of temperature and the development of the thermometer allows us to measure changes in energy.

The idea of the thermometer comes from the Zeroth Law of Thermodynamics. The Zeroth Law says if you have an object A that is in thermal equilibrium with object B (think of the two items having equal “hotness”) and object B is in thermal equilibrium with object C, then object A is in thermal equilibrium with object C. Thus, all three objects are in thermal equilibrium, all have equal “hotness.” Typically, we think of object B as a device that has a scale that provides us a means of communicating that “hotness” to someone else, i.e., the thermometer.

Using the thermometer, we can communicate changes in “hotness” or heat. Put a pot of water on to the stove. Using a thermometer, we can take an initial value. Add energy by turning on the burner (electric or gas), and we can watch the reading on the thermometer is increasing. The energy of the water is increasing due to the input from the stove. Based on our thermometer, we can say that the temperature increased. But, is it what describe as hot or cold. This is where we say that the terms hot or cold are relative. The initial pot of water could be cold, warm or hot. Add energy, then it is warmer or hotter than the initial pot, but it still could be cold, warm, or hot.

Language makes a difference, and in science, our definitions are essential for communicating the physical changes that are occurring. So, what is cold? In our case, it is a lack of heat as compared to something else. What is cold to one person may not be to someone else or compared to something else. Most of us agree that if the temperature outside is 5 degrees F, it is a cold day, but that same temperature be a very hot day on some other planet.

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