For example, I have a mirror that suction cups to the bathroom wall. If I use it without water, it falls after a few hours. But if I add a bit of water on the suction cup, it lasts for MONTHS.
In: Physics
Suction cups work by the shape of the cup forcing a vacuum underneath it, which causes air pressure to force the cup closer to the vacuum.
Unfortunately, if any air gets under the cup the vacuum is broken and the cup falls off.
Fortunately, glass is flat enough and suction cups are flexible enough that where they meet there is almost no room for air to pass through, so the vacuum can stay stable for quite a while.
Unfortunately, neither the glass of the mirror nor the material of the suction cup is perfect. The little bit of room for air to pass through will break the vacuum in a matter of hours most of the time.
Fortunately, water can be used to fill those imperfections instead of air. As long as the water is there (which can be months, since there’s no air to evaporate it) the vacuum will be protected.
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