Cut out some cardboard squares.

Peel back the cardboard.

Tape peeled edges together.

Sproing!

PDF Downloads
As a Pro member, you will gain access to download any Instructable in the PDF format.
You also have the ability to customize your PDF download.
Gone to my Blog, too:
http://faz-voce-mesmo.blogspot.pt/2012/07/behance-virtualizacao-e-molas-de-cartao.html
Many years ago, there was a nationwide paper industry ad campaign showing a car driving over a bridge made of cardboard. In case you need something to do in your spare time!