Friday Sprog Blogging: practical thermodynamics.

A conversation last Thursday, amid rain and wind, as we watched the elder Free-Ride offspring's soccer game:

Dr. Free-Ride: How are you doing?

Younger offspring: Brrr!

Dr. Free-Ride: Well, why don't you zip up both your warm layer and your raincoat?

Younger offspring: OK. Why does zipping them up keep you warmer?

Dr. Free-Ride: Well, what do you think?

Younger offspring: I don't know. There's a little space between my shirt and my warm layer, and between my warm layer and my raincoat.

Dr. Free-Ride: What do you think is in that space?

Younger offspring: Air?

Dr. Free-Ride: That's right. So, when you're zipped up, you're trapping those layers of air for your body to heat up.

Younger offspring: If my body is heating up the air, doesn't that make me colder?

Dr. Free-Ride: OK, but your warm layer and your raincoat aren't letting those toasty-warm layers of air escape once you've heated them. You're keeping them close to keep the heat near your body.

Younger offspring: Oh. But if I'm not zipped up, it can get away?

Dr. Free-Ride: Indeed. The wind could come and take that nice toasty-warm air and mix it up with all the other air out there.

Younger offspring: And leave me with cold air that my body has to heat up all over again.

Dr. Free-Ride: Yup.

Younger offspring: I don't want to have to keep heating up more air with my body when I'm already cold.

Dr. Free-Ride: So stay zipped up.

Younger offspring: Can I have your hat?

Dr. Free-Ride: Nope. You already have two hoods and I just have one. Besides, I'm not sure if I'll be able to drive you home if I'm hypothermic.

Younger offspring: It's OK, I was just asking.

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Walking to school on a cold morning: Elder offspring: I'm going to steal your warmth! Dr. Free-Ride: Oh really? Elder offspring sticks hands in Dr. Free-Ride's coat pockets, where Dr. Free-Ride's hands are. Elder offspring: Brrr! Your hands are really cold! Dr. Free-Ride: Yes, they are. Mwah ha…
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"It's okay. I was just asking!" Kids are great!

I'm looking forward to a future physics lesson about applied force and wind resistance.

Hi, I remember meeting you at the Seattle SciBlog meeting. I remember our younger offspring are the same age.

My 14 year old daughter quit playing soccer a couple of years ago. Though she has just shocked me by saying she agreed to join another soccer team. The trick is that it is INDOOR soccer.

So tomorrow instead of standing in wind and rain, we will be watching her play inside a former airplane hangar at a former Naval Air Base. Woo hoo.


A space between your shirt and your warm layer? Not exactly. What your clothes do is they trap air which your body heat then warms up. And you're always producing body heat, that's why we call mammals like you warm-blooded.

But it isn't just air between layers of clothing, it's also air in the layers of clothing. Air is trapped in among the fibers of your warm layer, and that is warmed up by your body heat.

Start with your skin, which radiates heat. Next to that you have your undershirt, which sops up or wicks away your sweat. (Yes, little girls sweat, it just doesn't stink or produce pimples and blackheads like big girl sweat.) Then you have your shirt, your warm layer, and your coat or jacket. All this traps air you warm up.

What makes warm clothes important for someone your age is the fact you have less body for your skin that Mom does. That is, Mom has less surface area for her volume than you do. It's part of why you can stay cooler than Mom on hot days, and why Mom can stay warmer than you on cold days.

Producing body heat also uses up the energy you get from your food. Cold weather means you have to produce more body heat. That means you have to eat more than you need to in hot weather, so you have a bigger appetite. Now think about your sister and the growth spurt she's going through. The growth spurt and all the changes. That's why she eats like a horse. When she turns 13 or so she's going to be eating like a starving horse. So will you when you turn 13.

Cuddling or snuggling (which is just like cuddling, only with blankets) with Mom or Dad also involves body heat. But also hormones and pheromones that make you and Mom or Dad feel good, friendly, affectionate, even sleepy. That's why they are also good things to do during cold weather.

So stay warm, cuddle when you get the opportunity, and be careful where you had a snack or treat. A stomach-that-walks (your sister that is) is a persistent and clever beast.