Place a coin on a flat plate. Pour enough water on the plate to cover the coin. Now remove the coin with your bare hands–without getting your hands wet or by pouring the water from the plate.
Here’s how to do it. Thoroughly rinse a clear, heat-resistant glass or mug with boiling water. (Warning: children should continue only with adult supervision)
Set the heated glass upside-down onto the plate next to the coin. Now watch what happens!
As the air in the glass to cools, water gets drawn into the glass. Wait a minute for the coin to dry–then pick it up without getting your fingers wet!
Understanding what happened isn’t difficult. When the glass was heated, the air in it expanded and some of the air naturally went out of the glass. Then the air began to cool and contract, but with the glass standing upside-down in water, there was no way for the lost air to flow back into the glass. The water under the glass, then, experienced a lower air pressure above it than the air on the plate. Water was, therefore, drawn up into the glass until normal air pressure was restored.