What is surface tension?
http://www.mocomi.com presents: Can you add objects in an already-full glass and not let the water spill? REQUIREMENTS Water A Glass Pins (different shapes & sizes) WHAT TO DO Fill up the glass of water right upto its brim. And then start dropping the pins into the water one by one. WHAT HAPPENS You will see that the water does not spill out of the glass even though it is filled right up to its brim. WHY THIS HAPPENS The surface tension of the water doesn't allow the water to spill out and is the key reason for holding the water in the glass although it is already full