Get a tall glass and a can of soft drink.

Put the glass and the soft drink in the fridge for several hours.

Get the glass out (not the drink yet) and stand the glass somewhere in a warm room.

Look carefully at the sides of the glass. Run a finger over part of the glass. The moisture you see comes from condensation. It was a gas in the air and now, because the air next to the glass has been cooled, it has changed from a gas to a liquid.

You didn't pour the drink in at first because we wanted to see that the condensation was due to the cold and not due to there being any liquid around.

Now pour the cold drink in. This makes the glass stay cold for longer and you should get enough condensation for drips to run down the glass. Oh, and enjoy the drink!