Under Pressure

Karyn (my wife) told me that everyone at home has been trying to pull apart these two plastic baby sipping cups that have been pressed together for days (not sure for how long). The smaller cup was so far inside the larger one, that there was no edge to hold on to.

two stuck together cupsI had an idea. I could put the two stuck-together cups into the freezer,freezer cups and fill a glass Pyrex bowl with water. I put the water filled bowl into the microwave for about four minutes. four minutes in the microwaveThen I drew a diagram on the dry erase board and called the kids to come over and explain how we could use the near-air-tight seal between the two cups to our advantage because we know that air expands when hot, but cold air has its molecules closer together. dry erase diagram of expanding gas within baby cupsI told them that my hypothesis is that when I put the cups full of cold air into the very hot water, the air will expand and hopefully push apart the two cups from within.

I also informed them about the danger of possible splashing of very hot water, so they moved back a little.

With two oven mitts on my hands, I put the steaming bowl of hot water on the dinner table, and retrieved the cold-fuzed baby cups to be lowered into the water. After mostly submerging the cups, nothing seemed to be happening, kids waiting for gas to expandbut after about 30-45 seconds, I felt a low vibrating squeaky almost-sound. I was now holding the top cup with my bare fingers. bubbles started to come up from the waterA few bubbles came up, and more squeaking Tupperware-like noises occurred. I asked each of the kids to place one finger on the upper cup to feel the vibration I noticed, since it was nearly inaudible. feeling for vibrations as the gas chamber expandsEyebrows raised, but it didn’t feel like the cups were moving any more to me. Once the vibrations seemed to be slowing, I feared that maybe too much air escaped around the seal between the cups to separate them.

I lifted up the top cup from the water, and the smaller cup fell out with a faint “puh” sound as the remaining pressure was finally released. (I guess the internal pressure of the cups was balanced with the external water pressure from being submerged)

I was relieved to be my kids science hero for the moment, knowing they all tried to pull apart these same cups unsuccessfully. I felt like this was too fun not to share. succesfully separated cups

Who says you won’t eventually use something you learned in science class? Not me.

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