Fluids

[ruffkilla]

As a stunt, you want to sip some water through a very long, vertical straw. what is the tallest straw that you could, in principle, drink from in this way?

[Doc Al]

Well, what do you think?

[ruffkilla]

well i know the answer is 10 m if you round gravity to 10 m/s^2. i also know that the pressure on the top of the straw is 0 Pa. but besides that i have no clue, thats why im asking it.

[Doc Al]

When you sip through a straw, what pushes the water up the straw?

[ruffkilla]

the vacuum created by sucking your cheeks in.
i came up with this solution.
P1 + rough (g) (h1) = P2 + rough (g) (h2)
P1=0, h1=0
so P2 = rough (g)(h2)
1 atm= 1000(10)(h2)
1.01 EE5=1.0EE4(h2)
h2= 10 m

but im not sure.

[Doc Al]

Looks like you've got it. It's atmospheric pressure that pushes the water up the straw. The maximum height of water that can be supported by the air will be found by setting the water pressure (\rho g h) equal to atmospheric pressure.