This section is from the book "The Boy Mechanic Vol. 1", by Popular Mechanics Co.. Also available from Amazon: 700 Things for Boys to Do.
Take a quarter and place it flat against a vertical surface of wood such as the side of a bookcase, door facing or door panel, and strike it hard with a downward sliding motion, pressing it against the wood. Take the hand away and the coin will remain on the woodwork. The striking and pressure expel the air between the quarter and the wood, thus forming a vacuum sufficient to hold the coin.
 
Continue to:
More: