The Four-eyed Dilemma

Dear Doctor Wizard,
I’m confused. I love to play outside in the snow with my friends, but when I come back inside, my glasses fog up. My friends who don’t wear glasses always pick on me when this happens until I can see again. My teacher says that fog is just water, so what gives? It’s cold and wet outside, but warm and dry inside – so why do my glasses that were perfectly clear outside where it’s wet fog up when I come in where it’s dry?
Signed,
Bespectacled and Bruised

Dear Four-Eyes,
First of all … those aren’t your friends. A friend would help you remove your glasses, then start thumping you.
Now that we’ve got that cleared up, let’s look at the science question.
It’s actually wetter inside than outside – at least there’s more water in the air inside than out.
Now before you go all ‘liar liar, pants on fire’ on me, read on. Even though it feels drier, there’s more water in the air in the nice warm cabin than there is outside in the cold. If there weren’t, your glasses would not fog up. 
Why is that? It’s simple really (at least if you're Doctor Wizard). For the same reason you can dissolve more sugar in warm water than you can in cold water (you knew you could do that, right?), you can ‘dissolve’—or evaporate, to use the correct term—more water in warm air than you can in cold air (in both cases, this is related to the kinetic theory of matter, but if you share that little tidbit with your friends, they’ll beat you up even more. Trust me – I know.  Dr. Wizard was young once too).  So the dry air inside your house holds more water than the wet air outside. You just don't notice it, because water dissolved in air doesn’t feel ‘wet’.
The reason that water forms on your glasses when you come inside is because your glasses are still cold – nearly as cold as they were outside. And because your glasses are still cold, the air that touches the surface of them gets just about as cold. In physics, this little microscopic layer of air on your glasses is called the ‘boundary layer’, and if the glasses are colder than the 'dew point' for the inside air, that means there’s more water in the air than it can hold, and it condenses into dew (which is why they call it the dew point) on your glasses. But as soon as your glasses warm up to room temperature (or at least above the dew point of the inside air), the dew evaporates back into the room air – and your friends better watch out. 
Extra Credit: Read this to your dad – then ask him if he can tell you why frost forms on that mug they pull out of the freezer for him down at the tavern – even though there’s no frost on it when it’s still in the freezer. If he hasn’t had more than a couple, he should be able to figure it out. 

Poindexter Points:  The defrosters in most new cars pull in outside air, and pass it through the air conditioner first, before running it through the heater, and finally over the windshield.  This makes the defroster much quicker and more efficient.  Ten PP's if you can explain why.

Beneath the Wings

Hey Doc,

I love that Bette Midler song, ‘The Wind Beneath my Wings’, but I really don’t get it. What does she mean when she uses that expression?
Signed,
Puzzled Pilot

Hey Puz,
Good question. As best the Wiz can tell, The Divine Miss M. is making two statements:
1. ‘You are a good friend, and I can always count on you.’
2. ‘I don’t know squat about aerodynamics.’

While we appreciate what she is trying to say—and love that gal to pieces—we feel compelled to help out with the science. As Bernoulli’s principle clearly states, it is the wind above the wings that provides the lift. To the extent that wind beneath the wings has any effect at all, it is to bring down the flying object (bird, plane or Superman) and—aerodynamically at least—to be a drag.  We feel certain that this was not the message she meant to convey. 
We encourage La Midler to continue her exemplary work entertaining us – occasionally moving us to tears of joy or laughter, but to leave science to the professionals… like Doctor Wizard.

Signed,
Your Well-grounded Doctor

Darkest Before Dawn?

Dear Doctor Wizard,
Hi!  Thanks for taking my question.  I think you're really cool, and read your blog all the time.
Okay, here goes:
Is it really always darkest before the dawn? 
Signed, Nightowl 

Dear Nighty,
First of all, don't be so damned obsequious.  Nobody likes a suck-up, and readers will assume you're a plant, tossing up slow pitches for me to hit out of the park.  Besides, you couldn't have read my blog before, since yours is the first question.
That being said ... good question!  My advice, never say 'never', and rarely say 'always'.  As comforting as the thought may be that it's always darkest before the dawn, reality doesn't need to conform to our comfort.  In the most literal sense, it is darkest before the dawn.  But one should not infer from this that it's darkest immediately before the dawn.  In the absence of artificial light (nearby cities, campfires, etc), and normalizing for the stage of the moon, it's actually darkest about midway from dusk and dawn, when the sun is directly opposite one's position on the surface of the Earth - midnight ... way before dawn.  
If you still want to find words of assurance for a friend in need, it is (normalizing once again for transient phenomena such as weather fronts, etc.) generally coldest before the dawn ... or soon thereafter.
I hope that helps.
Cheerfully,
Dr. Wizard