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Homework Help: Longest Straw

  1. Dec 5, 2005 #1
    I recieved a homework problem that I need guidance on where to start.

    What is the longest vertical soda straw you could possibly drink from?

    I do not know where to start on this problem. A small push in the right direction would be greatly appreciated.
  2. jcsd
  3. Dec 5, 2005 #2
    As I posted this I had a possible epiphany.

    p = [tex]/rho[/tex]gd

    If the depth at which the straw is submerged makes rho*g*d greater than 101.3 kPa than the water above the end of the straw keeps the water down. Although now I know that won't work because that is how deep the straw is not how long it is.
  4. Dec 5, 2005 #3


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    Staff Emeritus
    Science Advisor

    in TeX, write /rho as \rho to get the correct letter.

    Your approach is correct. One must identify the height (depth) of water, which gives a pressure drop of 1 atm, since it is assumed that the reservoir of water is at one atmosphere (101325 Pa) absolute, and the lowest pressure one could achieve is a pure vacuum of ~ 0 Pa.

    The only way to obtain a greater head of water is to increase the ambient pressure above 1 atm.
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