Idle Analytics» Thermo for Normals

Thermo for Normals (part 30): Complicated things

Reuben — Fri, 22 Feb 2013 19:50:24 +0000

All cars have to keep themselves cool. The reason for this, as we've seen, is the inefficiency of the engine: you can't convert the heat, made in the burning of gasoline, into work without creating some waste heat. If we take the energy stored in gasoline to be the "free energy" of the chemical bonds, …

Thermo for Normals (part 29): Radiation, continued

Reuben — Wed, 06 Feb 2013 05:40:46 +0000

Now we know the amount of radiation coming from an object with a surface at temperature . And we know the amount for each frequency of light. It's where is frequency you're interested in, is the speed of light, and is a property of the object called emissivity. Emissivity measures the fraction of white light …

Thermo for Normals (part 28): How things radiate

Reuben — Sat, 29 Dec 2012 04:47:51 +0000

Every object, including you, radiates all the time. The radiation comes in the form of light, also known as electromagnetic radiation. Most of the time, this light isn't visible. Right now I'm radiating, and almost all of what is coming off is infra-red (IR), though there is also a tiny amount of radio, and microwaves. …

Thermo for Normals (part 27): Diffusion and sound

Reuben — Fri, 07 Dec 2012 21:42:54 +0000

The other day, my wife cooked up some microwavable popcorn while I was down the hall in the bedroom. The sound of the popcorn being made traveled seemingly instantly, but it took a full 5 minutes before the buttery smell came down the hall. Why is one so slow and the other so fast? Both …

Thermo for Normals (part 26): A gas in detail

Reuben — Tue, 20 Nov 2012 17:30:03 +0000

A molecule in a gas is being knocked into by lots of surrounding gas molecules. This is a very complex, almost random-seeming process. And yet we know that at higher temperatures the gas molecules simply must be moving faster on average. There must be a relationship between the temperature and the average energy. Moreover, we …

Thermo for Normals (part 25): The odds of being (energy) rich

Reuben — Fri, 26 Oct 2012 04:13:42 +0000

In a gas such as the air you're breathing, not all of the molecules are flying around with the same speed. If they were, that would be pretty amazing. Nevertheless, most of the molecules are flying around at about the same speed. And the speed is related to the energy. We'd like to know what the …

Thermo for Normals (part 24): Some closing thoughts on the 3 laws

Reuben — Thu, 11 Oct 2012 05:30:54 +0000

At last we know all 3 laws of thermodynamics: Internal energy of a system increases when heat is added to it and decreases when it does work (). No cyclic process can turn heat entirely into work. Absolute zero cannot be attained. The first two of these statements encompass all of what we think of …

Thermo for Normals (part 23): Absolute Entropy and the Third Law of Thermodynamics

Reuben — Mon, 17 Sep 2012 04:49:04 +0000

Here I've been blabbering on and on about entropy, but all I've really talked about is changes in entropy. Irreversible things miss opportunities to do work, and that makes entropy go up. But what is the entropy of, for instance, a bottle of gas? It has pressure, temperature, volume, and internal energy. If the gas is …

Thermo for Normals (part 22): Other ways to create entropy

Reuben — Mon, 27 Aug 2012 06:26:26 +0000

I have to admit, I've been fibbing a bit. It is absolutely true that changing something's temperature by heating changes its entropy by . However, this is not the only way to change it. In fact, anything that's irreversible increases the entropy. And there are ways to decrease the entropy of a system without taking …

Thermo for Normals (part 21): Time reversal and breaking the 2nd law

Reuben — Mon, 06 Aug 2012 05:38:29 +0000

Suppose you are recording a video of someone playing billiards. The balls crash into each other, and if you sit down and calculate the energy and momentum of the balls before and after a collision you will find that energy is conserved and momentum is conserved in each collision. Now, if you reverse the video, …