## Thursday, December 10, 2015

The Physics of the Spikey Shower Curtain

I was getting my daily dose of internet nonsense and came across quite the interesting product. Below is a picture of a shower curtain that is designed to force people out of the shower after 4 minutes by slowly inflating spikes during the duration of the shower. My initial thought was “OH wow, I need this!” but soon thereafter I began to wonder about the physics of this shower curtain. As it turns out, even in the 21st century Bernoulli’s principle still inspires a plethora of products.

Bernoulli’s principle states that an increase in the velocity of a fluid leads to a decrease in the pressure of the fluid. Applying this concept to the shower curtain explains why the spikes inflate over the time one is in the shower. The curtain creates a barrier between the bathroom and the shower, which are of the same pressure before the water is turned on. Once the water is on, the falling fluid increases in velocity as a result of gravitational acceleration. This increase of the velocity of the fluid on the shower side of the curtain leads to a decrease in pressure as indicated by Bernoulli’s principle. There now is a pressure gradient between the shower and the bathroom, with the pressure in the bathroom being greater than that in the shower. The lower pressure in the shower cannot sustain the push of the pressure from the bathroom, resulting in the gradual inflation of the spikes caused by the greater pressure outside of the shower.