X-Mozilla-Keys:                                                                                 
Bill Freeman wrote:

Vance Jaqua wrote:

This is the old business card with a pin and try to
blow it off the spool - it will always float if there
is enough pressure, and the height and weight of the
plate are not scaler either - insufficient data !!!!
Vance

Will you send us a sketch of the card, pin and spool Vance?
I am not familar with that trick and I am kind of curious.

Are you sure it is the same situation as a plate floating
in a uniform flow field that is much larger than the plate?

Paul Lamar

Paul,

This trick is a std for my 6th grade science lectures. Take an
ordinary thread spool, a small piece of cardboard, say 2" square
and push a straight pin thru it near the center.   Put the pin
in the hole in the spool (it is only there to prevent the card from
sliding sideways too much) and then blow thru the spool.
If you want to examine the effect longer, tape the spool to
the end of your vacuum cleaner hose, running from the outlet
so it blows.

The card will lift off of the spool slightly and then stay right
there, regardless of the angle.  I do it with the airflow straight
down for most effect.  The high velocity air parallel to the
surface of the card provides the lift to keep it stuck to the
spool as long as there is airflow.  Intuition says that the
act of blowing on a card should push the card away, but
the turning of the flow to radially outward causes the
unexpected lift effect.

Bill

Ah so! Sounds like our situation is entirely different.
If I replace the aluminum with something lighter such as 
cardboard or paper it blows it away. Obviously the 
vertical flow around the edges of the plate make
all the difference. Jeff still wins and Ed gets a prize
for best calculations.

Paul Lamar
 
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