The refrigerator is entering lock-down mode!
Are you in a warm, dry environment? If so, go open your refrigerator door, stand there for a few seconds and get something out if you’d like. Wait a short while, another few seconds or so. Maybe long enough to pour a glass of water if you’re the kind of person who keeps that in your refrigerator. Now try to open the door to your refrigerator again. Feel that? It’s hard, or at least harder to open!
For those of you who are either not living in a desert or pretty much anywhere in the northern hemisphere at the moment this will probably not do much of anything, so I guess you’ll just have to take my word for it. But what you would be experiencing is the creation of a pressure difference between your kitchen and your refrigerator. The why isn’t particularly hard to understand, although it is a little unintuitive.
So, let’s start with a refrigerator, shall we?
The air inside is cold(er) and the air outside is warm(er), and dry. After opening the door, warm air is introduced to the interior, mostly by way of the closing door itself. Once the door is closed, the warm dry air cools rapidly. Cool air takes up less space than warm air (the same reason hot air balloons can fly), so what you wind up with is a rather surprising pressure difference between the inside of the refrigerator and the rest of the kitchen.
You might be wondering. Why dry air. Water takes up way less space than water vapor, so wouldn’t you get a stronger vacuum that way? Well, yes and no. If you had a really tight seal on your ‘fridge that could work. The problem is that the phase transition has an overhead so you’d need a bigger temperature difference to achieve the same effect and is also slower. The dry air is so effective because it can cool down and “shrink” rapidly compared to the rate at which pressure is exchanged by the seal on the door.
This was an incredible source of amusement while I was in Argentina for a couple of weeks. Someone would open the refrigerator to extract the bottle of water, say, pour a glass, then walk back with the bottle in hand to return it. Except the pressure difference was so great, it took two hands to open the door. An entire evening was passed trying to explain this physically, so I figured I had to share.
Tags: Science