# Shower curtain

Question:

When you turn on the water spray in a shower stall with a shower curtain, which way does the bottom of the shower curtain move? Does the bottom of the shower curtain get pushed out of the stall, remain stationary, or get pulled into the stall? Assume that the shower curtain is hanging without friction and that the water spray does not directly hit the curtain.

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C

A

P

T

A

I

N

I

N

T

E

R

V

I

E

W

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Solution: The obvious solution (wrong, naturally) is that the spray of the water pushes air out of the shower stall, forcing the shower curtain to be pushed out. If that happens, it’s because the pressure of the water is directly moving the curtain. When the water does not hit the shower curtain, air is pushed out of the shower stall, but the air escapes from the top of the enclosure (especially if it is a hot shower). The resulting low pressure at the bottom of the shower stall forces air in, the movement of which flutters the shower curtain toward the enclosure. A candidate who was posed this question, and failed to answer it correctly—and wasn’t offered the job—says he will never take another shower without being reminded of this job interview.

Solution: The shower curtain is pulled into the shower stall.