Mom takes vitamins every morning. They come in glass ampoules. She first has to break off a top on one side and then on the other side as well.
How come if she holds that ampoule with the open side down, that liquid doesn’t spill out until she breaks off the other tip too?
Answer
You will definitely learn that in secondary education. A short explanation, but there are several reasons at the same time actually. Water likes to stick to glass because of its love/affinity for that kind of surface. This is also called adhesion. But adhesion alone is not the explanation. Mainly it has to do with (under) pressure. After opening one side of the ampoule (and then pointing that side down), gravity pulls on the liquid inside. If you also open the top, the liquid will simply run out. However, if the top is still closed, the liquid sinks and creates a bottom part: the air above the liquid gets more space because the liquid descends. So the pressure is lower. A low pressure attracts things, as it were, and keeps the liquid in the ampoule. If you also open the top, the air pressure above and below the liquid will be the same, and gravity will recover: the liquid will still run out. Finally: create negative pressure yourself when you take a bath: you take the shampoo bottle, hold it upright, push in the sides, turn them over and submerge the opening. The negative pressure will suck water from the bath into the shampoo bottle.
PS: your mom may not like that diluted water shampoo is left over … but everything for science hey 🙂
Answered by
dr. Jan Buytaert
Biomedical Physics and Optics: *middle and inner ear mechanics *electro-optics *tomography *interferometry *3D imaging *endoscopy *image processing *profilometry *topography *programming *classical physics
Prinsstraat 13 2000 Antwerp
http://www.uantwerpen.be
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