This is a neat project to do to teach the girls how to use a jackknife.
From The Happy Scientist, Robert Krampf
This week's experiment is a trick that my Grandfather taught me when I was very young. He called it a "whistle stick", and making one brought back delightful memories from my childhood. It is a marvelous toy, made in a minute from a popsicle stick, but it is also an interesting science puzzle to solve.