How bad mornings go worse, demystified.
When you take your morning shower, you may or you may not have noticed how
the shower curtain sometimes seems attracted to you. While you try to escape the
first seconds of ice cold water spraying all over your sleepy cold body,
you somehow get a feeling that the shower curtain is closing in on you. Maybe someone
or something is outside the curtain, slowly wrapping it around you, as if
to engulf and suffocate you. Sometimes the wet and cold curtain will cling to
your body and your legs much like strange women do when you're not single.
Images from Psycho flash before your eyes as you wrestle and hope that it was
only a draft or something this time too...
This is perfectly normal, and nothing to be afraid of, it turns out. This
phenomenon has been discussed by drunk physicists for decades, but it's always
been a strictly theoretical discussion. Some blame the Bernoulli effect, which
is used for describing why airplanes can fly. But that's not really similar is
it? In the shower we have a stream of finite particles and a presence
of air standing still. Others claim that it because of some kind of buoyancy
effect, meaning that hot air will rise and produce a pressure difference that
will account for the shower curtain's behavior. Well, obviously this is wrong, since
the damn curtain attacks even before the water is hot!
Well, it turns out that all the money spent on research isn't wasted. David Schmidt, an Assistant Professor at the University of Massachusetts,
used a state-of-the-art fluid dynamics simulation program, in order to see
what really happens in the shower. This program will numerically solve the basic equations of fluids, with a trade of in
computer time against accuracy. The software can simulate spraying water, and
by some sort of FEM-like division of the shower area, it was possible to
render a reasonably accurate result, in a reasonably short time. These kind of
differential equations tend to be hard to solve, even numerically, and usually
require quite some time for even the simplest cases.
What really happens in that shower is that the water stream creates a
vortex of air. As you can see on the illustration below, the vortex
will rotate horizontally. The eye of the vortex is at lower pressure than the
surrounding room and the rest of the vortex. Compare with a cyclone. This low pressure virtually sucks the shower curtain right into the center of the vortex, which is also where you are likely to be standing.
One way to avoid this is to shower under lower water flow, so that the vortex
doesn't get strong enough. Another solution is to acquire an industrial
strength shower curtain, not easily affected by tiny household
|--< . /--<--\
| .. /---<---\
| .. / --<-- \
| ... / / -<- \ \
| .... \ | | o | | | <--- Vortex
| .... \ \ ->- / /
| .... \ -->-- /
| ..... \-->--/
| ..... \->-/
| ....... <--- Your shower
Brought to you in the spirit of Physics FAQ.
Source: Scientific American