The Paper Napkin Trick
It's a good idea to practice this trick, too, where spilled water won't do any harm.
- a paper napkin
- a plastic cup of water
What to do:
Drape the napkin over the edge of a kitchen counter or table. Place the plastic cup of water on one corner of the napkin about an inch (25 mm) from the edge. Pull the napkin quickly from under the plastic cup.
The napkin comes out-without your spilling any water.
The cup doesn't overturn because of the tendency of things at rest to stay at rest. It's that old law of motion-inertia-at work. If it does spill? You're not pulling the napkin fast enough or with enough force.