Fill a glass with water. Use a rubber band to hold a handkerchief tightly over the top. Over a sink, quickly turn the glass upside down. The water should stay in the glass.
The water didn't flow out of the glass because of a special property of water called surface tension. Water is made up of tiny molecules that act like magnets. They stick to one another, making a stretchy surface across each hole in the handkerchief. These surfaces hold up the water. Press gently on the handkerchief. You'll see water trickle out and air bubbles rise through the water as these surfaces break.
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