Okay, I don’t really have a #2 planned for this series, but you never know.
Here’s what happened:
On my roadtrip to Texas last week, I took along some low-carb food in case I had trouble finding it on the road (in the sense of restaurants; I’m not talking about roadkill!). Among the things I took was a carton of low carb milk that I had opened and didn’t want to go to waste. I could take this because the carton in question had a screw top cap and so wouldn’t leak all over the place.
So, over the next day, I finished the container of low carb milk and tossed it to one side, figuring I’d throw it away the next time I stopped at a motel.
But before I did so, I noticed that something had happened to the milk carton: It had swelled up and now looked like this:
What had caused it to swell up? I wondered.
It couldn’t be the few remaining drops of milk in the carton releasing gasses, I thought. There weren’t enough of them to produce this kind of dramatic swelling.
Then I realized: I’m in an area where the elevations are above 4,000 feet. I bet that’s the reason why the carton bulked up so much.
The air in it from when I finished drinking the milk was put in at a lower altitude and then trapped in there when I sealed the carton.
But the air at that lower elevation was denser and there was more pressure on the outside of the carton from the air surrounding it. Now that I was at a higher elevation, the surrounding air pressure was lower and the carton was expanding due to the pressure of the denser air inside of it.
Or that was my hypothesis.
So I decided to do a little science experiment.
Instead of throwing the carton away, I kept it for another night and looked at it again in Dallas, which has an altitude of less than 500 feet. If my thesis was right then the drop of 3500 feet should cause the carton to de-inflate.
The next night the carton looked like this:
As you can see, it’s un-swelled itself considerably!
In fact, its sides are a bit sucked in now, and this was without opening it or doing anything to release the pressure in it.
In case it’s easier to see the difference, here’s a side-by-side comparison of the two:
So there you have it! Science is all around us–even when you don’t expect it!
There’s also a bit of relevance here to humans: It ain’t just milk cartons that expand or contract based on the air pressures found at different altitudes. Humans do, too. Our respiratory system is largely open since we’re breathing in and out all the time. Unless we’re holding our breath, our lungs won’t swell up or swell down this way based on rapid changes in air pressure, but other systems in our body aren’t so open: Our circulatory system, for example contains a certain volume of blood that is relatively constant and is used to operating at a particular level of pressure, and the fluids in our tissues don’t go in and out of us as quickly as air does when we breathe in and out. So the blood and other fluids in our bodies will be subject to at least some expansion and contraction the way the air in this milk carton was.
I assume that’s at least part of what’s going on when folks experience
