Thingamabobs – May 22nd

I’ve always found that there are odd little thingamabobs out there in the world. Things that are just a bit “off.” I suspect that most folks would just shrug and move on when encountering these thingamabobs, but I’ve always found them to be worth a second look and further examination.

I like to think my attitude is a result of my retention of a child-like sense of wonder and awe at the amazing universe around us. Others just think that I’m “easily amused.” (They very well might be correct.)

Today’s example is a soda can that spontaneously became an “outie” instead of an “innie.”






I know that it happened spontaneously because I was holding the carton it was in when it happened. It was one of those twelve-packs that’s intended to fit into your fridge and dispense one can at a time. I had just gotten home from the grocery store, set the case down on the floor, and felt the case shudder and thump, with a quite audible metallic sound.

I assumed that one of the cans had ruptured and I was going to need to clean up lemonade from all over the kitchen. I hadn’t set the sodas down very hard or on anything sharp, but something had triggered some sort of reaction.

Opening up the case, expecting to find sticky soda spraying everywhere, instead I found all twelve cans to be quite intact and clean. Eleven were perfectly normal, with both ends in the usual concave configuration. This one can had both ends pushed out to be convex.

From an engineering and science background, it made sense that this could have happened. The reason the ends are concave to begin with is because that  shape is very structurally sound to resist and contain the internal pressure from the soda’s gas. This is particularly true on this kind of can which is formed from a single piece of aluminum.

But having the ends concave (“innie”) is only one solution to the structural strength equation. An equally valid solution is to have the two ends convex (“outie”). Think about other large tanks used for containing volumes of liquid or gas under pressure. The Space Shuttle’s external tank. The tanks at the gas station or in your back yard that contain propane. The trucks that haul cold, liquid gases such as nitrogen or oxygen. They’re all shaped like long, narrow tubes with convex ends.

The fact that the huge, industrial strength containers use the convex ends makes me think that it might be because that configuration is stronger than the convex design. I might have to dig out and dust off some math textbooks to test that. (Ed. note: I won’t, don’t worry – I said might.) But the convex shape doesn’t lend itself to containers that can need to stand up on the ground or be stacked.

Think of fire extinguishers, or those big steel containers that contain helium for blowing up party balloons. They’re all flat on the bottom to make them easy stand up, but inside they’re rounded. (Convex or concave? Sounds like a question for “How It’s Made.”)

For soda cans, it’s a huge benefit if they can be stacked and stand up on their own. They also only have to withstand fairly low pressures. The solution there is to make both ends concave. Which is why they’re that way…

…until that rare moment when something snaps on one can and it flips from one stable configuration to one that might be slightly more stable from a pure standpoint, even if it does make it impossible to stand the can on its end.

It’s still amazing to me that it can do that without splitting open the aluminum – but there’s your proof.

(Kevin MacNamara, a high school friend, was the first to point out that I am “easily amused.” See, I still haven’t proven him wrong!)

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Filed under Curiosities, Paul

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