Science In Real Life

Continuing with our intermittent theme of being weather related, whether or not it’s the current weather, today’s topic is cold. Grab a hat and scarf, it’s about to feel very chilly. Lesson number one about cold is that there is no such thing as cold, only heat and the absence of heat. But scientists are lazy, so we use ‘cold’ as a shorthand for ‘lack of heat’. So we’ll start with heat and work our way back to cold.

What is heat? To answer that question, we first have to answer this one: What is matter? Matter, the stuff we all know and love and are composed of. Whether it’s electrons, protons, or neutrons, it doesn’t, er, matter – it’s still matter. The key point is that it exists in the form of lots of separate little subatomic particles (the aforementioned -ons). Each of those particles has a whole world of physics unto itself, much like Hollywood action movies.

What we’re interested in is the fact that (with certain constraints) the particles can move independently. So let’s put them together into atoms, since very few of us encounter more than a few stray electrons during the course of our daily lives. So we have a bunch of atoms, just sitting around, hanging out, maybe watching CSI, right? Wrong. Atoms are constantly moving, all the time. You can see this in a related effect known as Brownian motion, which you can see illustrated in this nifty Java applet.

Okay, so we have a bunch of atoms bouncing around like a bumper car ballet. So what? Well, they’re constantly exchanging energy with one another. Suppose one of the atoms happens to be sitting still. Pretty soon another atom with some sizable velocity is going to come along and whack it good. After that happens, they’ll both be moving, but with less velocity than the one atom originally had (this is conservation of energy in action).

So it’s not a stretch to say that all the atoms are moving with about the same speed – if any of them were significantly out of step with the rest, it would be brought back in line faster than a Republican congressman with a gay sex scandal. Now, it turns out we can relate that common velocity value to the temperature of these atoms. This should be fairly intuitive, but here’s another example anyway: you put a pot of water on the stove and turn on the burner I hardly know ‘er. At first the water just sits there, but when it’s boiling you can see the escaping steam (lots of very tiny and very hot water droplets) fly away. If the entire mass of water instantly turned to steam, all the atoms would be flying away from each other and into the air.

Now, we have one final link in this chain of thought before we can get back to cold. As you put more energy into a group of atoms, not only do the atoms move faster, but more and more they start to go in different directions. This touches on a very complex subject in physics called entropy, a proper explanation of which is so far beyond the scope of this essay that if this essay exploded, the proper explanation wouldn’t hear the sound for three days. Suffice it to say that when the atoms have more energy it’s easier for them to become disorganized, out of order with each other. And that right there is our final link.

To put it as simply as possible: Heat is disorder, cold is order. Why does something feel cold when you touch it? Because heat is being transferred from your hand to the object. Your atoms, bouncing around with heat, bump into the atoms of the cold object, causing those atoms to bounce around more than they were before – and as a result, your atoms bounce around less. It’s an energy transfer so direct it makes your online banking system jealous. When something feels hot, the reverse is happening.

So why is it so damned cold outside in winter? Because the molecules in the air have become more ordered. Well, relatively speaking. They’re still moving around quite a bit, but because they are moving around together they will steal energy from your atoms when they collide with you. Textbook gang violence behavior, really.