Why isn't water staying in a cup when I turn the cup around even though the air pressure has enough force to hold the water's weight? - Quora
![Atmospheric pressure experiment using a cup with a fluid to hold a glass plate - Physics Stack Exchange Atmospheric pressure experiment using a cup with a fluid to hold a glass plate - Physics Stack Exchange](https://i.stack.imgur.com/u8BIv.jpg)
Atmospheric pressure experiment using a cup with a fluid to hold a glass plate - Physics Stack Exchange
![Take a glass and fill it up with water up to the brim. Make sure that there are no air bubbles. Take a thick, stiff piece of cardboard and put it over Take a glass and fill it up with water up to the brim. Make sure that there are no air bubbles. Take a thick, stiff piece of cardboard and put it over](https://haygot.s3.amazonaws.com/questions/802383_fc0005281f5541a7a4f97c905f1c50c0.jpg)
Take a glass and fill it up with water up to the brim. Make sure that there are no air bubbles. Take a thick, stiff piece of cardboard and put it over
![Physics Reference: Air is trapped inside a glass bulb which is immersed in water and attached to a U-tube containing mercury. Physics Reference: Air is trapped inside a glass bulb which is immersed in water and attached to a U-tube containing mercury.](https://1.bp.blogspot.com/-8jNOmD09Dko/XoTTp5qvdaI/AAAAAAAAKyU/ELkXrrMTJag84_gQAUp08Q_QH0FFjeTgACLcBGAsYHQ/s1600/nov2017p12q15-pressure-trapped-air-glass-tube.png)