- Having your shower curtain stick to you can be a pesky nuisance.
- The reason behind this annoying phenomenon is the "Bernoulli Effect".
- The physics behind this effect also explains, in part, how airplanes stay airborne.
What these temperatures call for is a nice, refreshing shower — if only it weren't for that pesky shower curtain closing in and clinging to you the moment you hop in and switch on the water. Why does this happen?
The answer to that question lies in physics.
"Since a shower curtain is large yet light, it reacts to a small vacuum created in the shower cabin," Ohle Claussen of the Max Planck Institute for Dynamics and Self-Organisation explained to Business Insider. At least two physical effects cause this when you shower.
The vacuum sucks the curtain into the shower cubicle.
You can easily create a similar vacuum yourself by taking a thin piece of paper or a receipt and holding it to your lower lip. If you blow hard now, the note will not be pressed down, but will raise. Andreas Baumer of Business Insider tried it, as you can see in the above photo.
What he experienced is called the Bernoulli effect, which is part of the reason why airplanes can fly. It was the mathematician Daniel Bernoulli who noted that, in a space where the flow velocity is higher than in its surrounding environment, the air pressure there is always lower compared with its surroundings.
So if you blow over the paper strip, the speed of the air there is higher than under the paper, because the air below is, at most, moving only very slightly. This reduces the pressure of the air above the paper, creating a vacuum that sucks the sheet upwards. Your "over-friendly" shower curtain can also be attributed to this phenomenon.
Air from outside flows in and a pressure drop occurs
"When air enters the area of higher flow velocity, it must be accelerated in order to adapt to this velocity," Claussen explained. "In fluid mechanics, such an acceleration is combined with a pressure drop as the driving force. The additional kinetic energy the air particles receive is as a result of the fact that the higher air pressure in the area of slow flow works on these air particles when they reach the area of faster flow".
So pressure and speed are always connected where air flow is involved. The place of highest speed is also always the place of lowest pressure. "So if your shower head emits water at high speed in the shower cabin, the air in the cabin is carried away," says Claussen. "Consequently, air must flow in from the outside and be accelerated, resulting in a drop in pressure."
David Schmidt, a scientist from Massachusetts, highlighted a second cause for the negative pressure, using a computer that simulated the movement of water droplets. It showed that splitting water droplets in the lower part of the shower create a vortex that also contributes to negative air pressure.
So how do you stop your shower curtain sticking to you?
This effect is almost as great as the Bernoulli effect, according to Claussen. And the discovery was only made in 2001. This shows how small the occurring forces are but as the shower curtain is simultaneously large and light, it can be carried away by even the slightest dip in pressure.
The closer the air brings the curtain to the person in the shower, the more the Bernoulli effect is enhanced: "The same amount of air must now flow through a smaller gap and must therefore flow even faster in that small area. This increases the negative pressure at the point of approach until contact occurs.
The real question is: what can you do to put a stop to your overly affectionate shower curtain's embrace? Try attaching some weights to the curtain's base, inserting a lead tape through the hem, sticking the curtain to the tub with water or avoiding pulling it across so it's taut when you shower!
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