If you blow over a piece of paper, it actually lifts
up. This is caused when air flows over a surface and its speed increases
and its pressure decreases. This is the Bernoulliís Principle and
it explains how an aircraft wind can generate a lifting force, just like
in the piece of paper. Daniel Bernoulli in the 1700's first developed
different aerodynamic principles that helped explain not only planes but
why roofs can just lift off a house during a hurricane.
By blowing hard and steady, you can demonstrate a
version of Bernoulliís Principle. With a piece of straw and ping pong
ball, you can demonstrate magical "floating. You need to shoot a
stream of air directly up, as in the diagram. You can use a hair dryer
if you are doing this at home. The air is in rapid motion. Its pressure
is lowered. The floating ball is actually kept in place by the column of
upward rushing air. If it wobbles, the "jet stream" on either
side, forces the ball back to its optical illusion.
There are many tricks that you can perform with
air. These exercises are meant to open your eyes to explain the
mysterious "ghosts" that open and close doors in your house.