Why do the drapes move in?
Ok, so we know that air moves from areas
of higher pressure and temp to areas of lowers
ones. So when its cold outside and you open a window
in a warm room, the warm air (higher energy) flows out
the window to the colder air (lower energy),
if the net air flow is OUT the window, why do the drapes
The warm air flows out the top of the open window, the cold air comes
through the bottom of the window. The net air flow is zero, otherwise
your house would turn into a vacuum or blow up!
Gravity may be the answer. Imagine any given point on the verticle drop of the
curtain, the points of the curtain near the floor will have the least wieght to support
and be more flexible as a result. Even though air is flowing out and in
equally, the bottom of the drape will be more easily moved as the cold air
falls and hits the floor; thus making it appear the the drapes are tending to move
inward. A closer examination of this process will indicate that the curtain
will move toward the window with less motion at a point near the top of the window opening.
At this point the curtain contains more weight and therefore more inertia to resist
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Update: June 2012