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## Main Question or Discussion Point

I am wondering why a shower curtain is pulled inward when you turn on the shower.

Yes, I have read the classic answer that this is due to Bernoulli's law: the water makes the air move, and moving air has a lower pressure. Only, this does not make any sense at all if you know anything about how Bernoulli's law works.

Bernoulli's law is about conservation of energy along the flow of a fluid or gas. Once you start adding energy to the system (through a pressurized spray of water, for example), it becomes completely invalid.

I'll enter into a bit more detail: Bernoulli's law basically says that, if air speeds up along a line of flow, something must have made it speed up, and this "something" can only be a pressure differential. Accelerating air parcels must have a lower pressure in front of them to make them speed up. Write this down mathematically, and "half rho v squared" pops out pretty easily. But in the shower, the air was not accelerated because of a lower pressure in a particular direction, but because of the water being sprayed under pressure into the shower! There is absolutely no way whatsoever you can still use Bernoulli's law in that case.

So, why is the shower curtain

Yes, I have read the classic answer that this is due to Bernoulli's law: the water makes the air move, and moving air has a lower pressure. Only, this does not make any sense at all if you know anything about how Bernoulli's law works.

Bernoulli's law is about conservation of energy along the flow of a fluid or gas. Once you start adding energy to the system (through a pressurized spray of water, for example), it becomes completely invalid.

I'll enter into a bit more detail: Bernoulli's law basically says that, if air speeds up along a line of flow, something must have made it speed up, and this "something" can only be a pressure differential. Accelerating air parcels must have a lower pressure in front of them to make them speed up. Write this down mathematically, and "half rho v squared" pops out pretty easily. But in the shower, the air was not accelerated because of a lower pressure in a particular direction, but because of the water being sprayed under pressure into the shower! There is absolutely no way whatsoever you can still use Bernoulli's law in that case.

So, why is the shower curtain

*really*being pulled inward?