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Syringe Physics

  1. May 10, 2009 #1
    Can someone discuss the physics behind pulling air into a syringe, inserting needle into med vial, expelling the air, and finally drawing up medication. This process makes it easier to draw up the liquid med as opposed to simply inserting needing and drawing up med. Thank you.
  2. jcsd
  3. May 11, 2009 #2
    It provides a volume of air to replace the volume of liquid being withdrawn from the med vial. Without this, the withdrawal of the medical would be producing a partial vacuum in the vial.
  4. May 11, 2009 #3
    Air is never pulled into the syringe, only pushed in. Air goes from higher concentration to the void you are creating inside the syringe.

    If you put a vacuum gage on the syringe,(no matter how long the syringe was), The pressure differential would never exceed 14.7psi.(Sea Level)
    Last edited: May 11, 2009
  5. May 11, 2009 #4
    Yes, it is just a bit hard to corral those molecules and drag them in. You just have to let them follow at their own pace. Just like herding cats!
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