Why is that when you're drinking something with a straw, and then cover the one hole with your tongue or finger, and take the straw out of the drink,

Why is that when you're drinking something with a straw, and then cover the one hole with your tongue or finger, and take the straw out of the drink, the drink stays in there, even if the open end is facing down?

ANS: Air pressure pressing on the liquid at the bottom of the straw is enough to support the weight of the liquid. You can support up to about 30 feet of water by this method. After this, the air pressure is not enough, so the water falls down, leaving a partial vacuum at the top between your finger and the top of the liquid.