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

Something I noticed about eye droppers

  1. Nov 25, 2005 #1

    Pengwuino

    User Avatar
    Gold Member

    I've noticed something a bit odd when I use an eye dropper in one of my labs. If I pull up water near the middle of the container, the water will fill up to a certain level. Now if I bring the eye-dropper down and touch the buttom (effectively putting it in a position to suck up the wall of the container) but allow it a small area to actaully suction up some liquid, it seems to be able to fill 50% more then if I allowed it to create a suction in say, the middle of the container. I don't understand... what's causing this?
     
    Last edited: Nov 25, 2005
  2. jcsd
  3. Nov 25, 2005 #2

    Danger

    User Avatar
    Gold Member

    Sounds kinda weird. Are you sure that you're squeezing the bulb the same way in both cases?
     
  4. Nov 25, 2005 #3

    Pengwuino

    User Avatar
    Gold Member

    Yah, I was able to replicate it multiple times.... pretty weird....
     
  5. Nov 25, 2005 #4

    Danger

    User Avatar
    Gold Member

    Sure... :rolleyes: You just had to come up with this after Clausius split. He'd probably know it right off.
     
  6. Nov 25, 2005 #5

    Pengwuino

    User Avatar
    Gold Member

    whose clausius :D some sorta greek god?
     
  7. Nov 25, 2005 #6

    Danger

    User Avatar
    Gold Member

    Some of us think so. :biggrin:
     
  8. Nov 25, 2005 #7

    Pengwuino

    User Avatar
    Gold Member

    Oh and it seemed like it was the same crap that would happen when i worked with a pipet! I'd need to nearly apply the suction to the bottom to get any fluid to suction up.
     
  9. Nov 25, 2005 #8

    brewnog

    User Avatar
    Science Advisor
    Gold Member

    It's just the pressure differential between the middle and the bottom of the container from which you're drawing the liquid. Remember that you're not 'sucking' water up, you're providing a partial vacuum, allowing atmospheric pressure to 'push' liquid into the pipette. At the bottom of the container, you have the additional head provided by the extra depth of water.

    Think this is sound, hope I've not missed anything, I'm shattered.
     
  10. Nov 25, 2005 #9

    The pressure at the bottom of the liquid is greater than near the surface. Since you create a low pressure area in the eye dropper by squeezing the bulb fluid taken from the bottom where there is more pressure will result in it taking more liquid into the dropper.

    You will probably notice that when you push the dropper to the bottom that some fluid gets into the dropper even before you release the bulb. This is because of the greater pressure at the bottom. As soon as the dropper breaks the surface the pressure builds up inside it and compresses the air in the dropper. This makes room for more water. You will probably also notice that as you bring the dropper out of the fluid that some water escapes as the air in the dropper expands and pushes it out.

    Edit: I was beat to the punch by brewnog.
     
    Last edited: Nov 25, 2005
  11. Nov 25, 2005 #10

    Danger

    User Avatar
    Gold Member

    Wouldn't you just know it... I thought of that as a possible explanation (but wasn't sure there'd be enough differential), and the gf's stupid computer froze up before I could post it. :grumpy:
    I'm at work now, so as long as my boss isn't using this one, I should be okay.
     
  12. Nov 25, 2005 #11

    Pengwuino

    User Avatar
    Gold Member

    Yah i just realized this last night while i was trying to get to sleep, thanks anyways :P
     
  13. Nov 25, 2005 #12

    Danger

    User Avatar
    Gold Member

    Sleep? You were going to sleep? What the hell were you thinking of?
     
    Last edited: Nov 25, 2005
  14. Nov 25, 2005 #13

    Pengwuino

    User Avatar
    Gold Member

    it was 7am >:( ROAR!!!!!!
     
  15. Nov 25, 2005 #14

    Danger

    User Avatar
    Gold Member

    Alright, then... you're excused. Carry on.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?