What’s kind of weird, if you think about it, is that going one way is much harder than going the other way. Making stuff warm isn’t a problem. Just about anything you do will cause something to increase in temperature, even if you don’t want it to. But making stuff cold is trickier.
That seems surprising, because we think of temperature as a dimensional thing, where you can just raise or lower the level—the way you use a slider control to adjust the brightness of your screen. But that’s a false comparison, as you know if you have a thermostat in your house: At some point in the spring, you have to switch it from furnace to AC. They’re two different processes.
I’m going to look at a bunch of different ways that humans have invented to increase or decrease temperature. But first we need to talk about what the heck temperature is. No, it’s not a dimension. It’s something much more complicated. And it’s probably not what you think it is .
The change in thermal energy of an object depends on three things: the object's mass, the change in temperature, and the specific heat capacity (which depends on the material). In order to calculate the change in thermal energy, I need the specific heat capacity for the two materials (water and copper).
What Is Temperature Really?
My favorite definition is this:
- Temperature is a quantity that will be the same for two things that are in contact for a long time.
If you put a fresh, hot cup of coffee on the table, and then get distracted by something on social media, the coffee will soon have the same temperature as the table. Gah! They won’t have the same amount of thermal energy, but they will have the same temperature.
Right. Then what about thermal energy? This goes along with another rough definition of temperature:
- Temperature is a measure of the average kinetic energy of the particles in an object (where kinetic energy depends on both the mass and the velocity).
It’s not crazy to think of thermal energy as the sum of all the kinetic energies of the particles. (I’m oversimplifying a bit.)
But the main point is that two things can have the same temperature but different thermal energies. If you put pizza on aluminum foil in the oven, they will both reach the same temperature. However, the foil is very low mass and has much less thermal energy—that’s why it doesn’t burn your hands when you pull it out.
Did you notice I haven’t used the word heat here? I avoid this word because people think they know what it means, and it hinders their understanding of thermodynamic situations. We normally use it as a verb: The sun heats up our bodies. You heat the water to make tea. But it’s also used as though it were an actual thing that we can move around. We (stupidly) say “add heat” or we talk about “heat transfer.” Technically speaking, you cannot “bring the heat.”How to Make Stuff Hotter
There are many different ways to increase the thermal energy of something. But basically there needs to be some kind of energy transfer. Let’s look at some of the ways this can happen:
Shine Light on It
One way to transfer energy is with electromagnetic waves. Visible light is one type of electromagnetic radiation; there’s also infrared, x-rays, gamma rays. These are all the same type of waves but with different wavelengths. And they can all transfer energy.