An experiment on pressure and surface tension
an experiment on pressure and surface tension can also be used to make a whole person (
A drink bottle filled with water seems to have no problem, but when you unscrew the top of the bottle, you will see that it suddenly starts to leak.
practice: first fill the beverage bottle with water, tighten the cap, and then pierce a small hole with a pin near the bottom of the bottle. At first, these small holes actually leak a little, but after a little while, you can see that the leakage has stopped. At this time, although there are holes in the bottle, it can keep the water from flowing out. After unscrewing the cap of the bottle, you will see the fine water spurting out of the small hole.
principle: when part of the water flows out, the pressure in the bottle that tightens the bottle cap will decrease a little, and the water can not continue to flow out. After opening the bottle cap, the internal and external air pressure is balanced, and the water pressure will let the water flow out of the small hole. In theory, when there is a hole in the bottle, there should be air bubbles into the bottle, if the bubbles do come in, then the air pressure will become balanced and the water will continue to leak. But if the diameter of the hole in the bottle is small enough, the entry of bubbles will be hindered by another factor-the surface tension of water. When bubbles are formed, it is necessary to form a curved concave liquid surface locally, and affected by the surface tension of water, the liquid surface always tends to retract, so there is resistance to the formation of the concave liquid surface, and the smaller the scale is, the greater the resistance is.
Note: in order to successfully prevent bubbles from entering the bottle, the diameter of the keyhole must be small enough. I tried it. The pin on the left is OK, and the one on the right is too thick to succeed.
in addition, water leaks when squeezing the bottle, so a hard beverage bottle that is not easy to squeeze is better. Also pay attention to stay away from electrical appliances and other items that are afraid of water.
another experiment with similar principle: when you were young, you may have seen a classic air pressure experiment in which a cup /jar is completely filled with water, the cup mouth is covered with a card, press and hold the card over, the atmospheric pressure will hold the card and the water will not flow out. If the sealed thing is changed into a mesh small enough, the upside down will not leak, and it is the surface tension of the water that prevents the bubble from entering.
(the question picture is randomly found, but it has nothing to do with the content)
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