Physics/Cap bursting off tube
Hi. I hope you can help me. I am not a student; this is a real-life situation, which I should like to understand clearly. I have three tubes of dental tablets stacked on my kitchen window cill. Yesterday I heard a noise and found one of the caps had burst off, hit the cupboard some three feet opposite (it's a very small kitchen) and landed on the floor. The tube was half full. Putting the cap back on I realised something must have released some force to do that. The only explanations I can offer are that I live near a railway line so vibrations do cause things to move in this house, but more recently I have plugged in a mouse deterrent with ultrasonic and electromagnetic waves. I was wondering about the wisdom of this device since my bed is on the other side of the wall where this is plugged in. However, that's not my concern, my question is what forced the dental tablet tube to burst off on its own. There was of course no one in the kitchen at the time. I would greatly value a clear and accurate idea of what caused this 'explosion'. Many thanks. Best regards
That is a mystery, but it's definitely not from your mouse deterrent. You'd see far more severe effects elsewhere if that were the case. Ultrasound is typically in the sub-centimeter wavelengths, and the effects on your tube would have been immediate and noticeable if there were some sort of resonance forming within it. The fact that it happened over time, with no one around, says that some slow process happened inside. Much like wine that undergoes a secondary malolactic fermentation (where the malic acid is converted into alcohol) will sometimes push a cork out of a perfectly good bottle of wine (the CO2 byproduct doing the pushing), we probably can look to a chemical reaction here.
I'm not a chemist, but dental tablets most likely function via some sort of chemical breakdown reaction, perhaps activated by moisture. When they were last opened, you might have breathed in their direction, or perhaps you had just made tea...or even if it were just a humid day. Moist air seems to be the prime suspect. The moisture could have had a very very slow reaction, first pressurizing the tube enough to seal tight, then further (over time) pressurizing it enough to burst the top. That's really the only explanation I can think of. Perhaps if you knew their composition, you could ask a chemist. They might be better equipped than a physicist to tell you about the specific reaction. Aside from temperature change (are they in a window where they could get direct sunlight for a contributing factor?), I'm having trouble seeing another explanation.