Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Straw Sucktion

  1. Jul 16, 2006 #1
    Hi, I was wondering if anyone can tell me the reason why do we need to suck harder to drink a can drink when 1 straw is out of the drink and 1 straw is in the drink than when we suck the 2 straws while the 2 strws is in the drink?

    Sorry For the bad english... I'm from asia you see...
  2. jcsd
  3. Jul 16, 2006 #2
    What do you mean harder ? I have never had such an experience:confused:
  4. Jul 16, 2006 #3


    User Avatar
    Gold Member

    If one straw is out of the drink, you are losing the negative pressure (relative vacuum) in your mouth because of leakage through that straw and you will have to work harder to get a given amount of fluid up through the straw that is submeged. If both straws are in the liquid, a modest amount of effort will get your drink to your mouth in sufficient quantities, because without the air leakage, you will be more easily able to generate the vacuum necessary to draw the fluid up the straws.
  5. Jul 17, 2006 #4


    User Avatar
    Homework Helper

    Drinking through a straw is accomplished by reducing the pressure on top of the liquid in the straw by sucking on it (removing some of the gas). The higher atmospheric pressure on top of the liquid in the can then pushes the liquid upwards in the straw. This is somewhat similar to pressurized spray cans, except that the pressure in the can is higher than atmospheric pressure forcing the contents out when the valve is opened.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook