Just a simple question : when we remove a stopper of an upside-down bottle, water flows out. But the pressure caused by the mass of water's column is usually smaller than atmosphere pressure unless we use 10m height bottle. How could water flow out?
sorry for stupid question…
[Physics] How could water pour out from upside-down bottle, unless its pressure is smaller than atmosphere pressure
fluid dynamicswater
Best Answer
If the mouth of the bottle is small (e.g., a wine cork with drilled hole for a drinking straw), water indeed won't flow out. Would you also wonder why the water doesn't stay in an upside-down bucket (the limit case for a bottle with a very wide mouth)?
What happens is that air enters through the mouth with a volume equal to the volume of water that leaves the mouth. If you start with a flat water-air interface surface that is perpendicular to the mouth, the surface has to deform. With small openings, the surface tension of the water will win from the gravitational pull on the water surface. With a big opening, gravity wins.