What you need:

• A pocket handkerchief
• A small glass or tumbler
• Some water (in a bucket, bathtub, pond, or any other large container you like)

What you do:

1. Stuff the handkerchief in the glass so that no part of the handkerchief sticks out above the rim.
2. Turn the glass upside down and lower it straight down into the water, then raise it back up and remove the handkerchief. It will be completely dry.

What happened?

Air may be invisible, but it still takes up space. When you lower the handkerchief straight down into the water, the glass and the water enclose the air so it cannot escape upward. The air and handkerchief take up all the space in the glass, so the water cannot enter.