Here’s a teaser that’s a favorite of engineering students.
On a hot summer day, can you cool your kitchen by leaving the refrigerator door open?
The answer is nope. If anything, that will actually make your kitchen warmer, not cooler.
But how can this be? I thought you’d never ask.
The fact is, there is really no such thing as “cold”. It’s merely the absence of “heat”. Refrigerators don’t actually make things cold, they just remove the heat from them. And all that heat energy has to go somewhere. So it’s usually just dissipated back into the room. Ever wonder why the coils on the back of your refrigerator are so warm? That’s because they’re busy getting rid of all that heat.
If you leave the door open, the refrigerator will have to work harder because it will have to remove the heat from the entire room, not just the inside of the refrigerator. And it will put the heat right back into the room, making it warmer.
That’s the principle on which heat pumps work. They’re just air conditioners in reverse, removing the heat from the outside and depositing it in the house. In the summer they reverse the cycle and take the heat out of the house and put it on the rose bushes next to my front porch. (Oh, that’s why those bushes always look, uhm, tuckered out.)
Here’s something even better. A ceiling fan doesn’t make a room cooler. It just moves the air around. Moving air over our sweaty body feels cooler than stagnant air on our stinking body.
Actually, our engineering friends will tell us, it’s possible that a ceiling fan will make the room warmer, because the fan motor is generating heat, which it then distributes around the room. Oh, great, that made me feel better.
Engineers also like to talk about the fact that helium balloons don’t actually rise. Rather, the heavier air “pushes” them up. That’s a subtlety that escapes most of us romanticists. Next thing they’ll be telling us is that the Man in the Moon isn’t really winking at me.