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Strange Observation of Ink in Ball Point Pen

  1. Aug 29, 2010 #1
    I observed something odd this evening.
    When I inverted my ball point pen (writing side upwards-perpendicular to the ground level), there was no change in the level of ink. To my surprise, the ink started coming downwards (towards the open end of the refill) when I wrote with it ( inverted ) on an inverted book. If gravity is the reason for this, then why the ink did not move downwards in the first case?
    thanks
     
  2. jcsd
  3. Aug 29, 2010 #2
    try this inverted ball point pen on evening and come on the morning to see what will happen.
    actually you will see ink go downward away from the point pen.
    this happen because the ink of your point pen has high viscosity which will prevent ink from moving easily.
    moreover, if you see the tube of ink you will see it is close from other side.
     
  4. Aug 29, 2010 #3
    Please make it clear I did not get you
     
  5. Aug 29, 2010 #4

    Andy Resnick

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    I wonder if it's because you were letting air in as you rolled the ball.
     
  6. Aug 29, 2010 #5
    That's my take on it as well.
     
  7. Aug 30, 2010 #6
    Thanks...that is a satisfying explanation :)
     
  8. Aug 30, 2010 #7
    The vibration might have something to do with it, too.
     
  9. Aug 31, 2010 #8
    Vibration of what?
    the ball is smooth and doesnot impart vibrations to the pen.
     
  10. Aug 31, 2010 #9

    Borek

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    When you write pen is slightly moved/shaken, these are vibrations JD mentioned.
     
  11. Aug 31, 2010 #10

    sophiecentaur

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    On this small scale of things, the inter-molecular (electric) forces may well dominate and gravity may be of secondary importance. The action of the ball on the paper may have been to draw the ink up out of the tube (pull) and overcome any 'weight' forces.
     
  12. Aug 31, 2010 #11

    Borek

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    Just checked with some random ball pen that I had on my desk - it worked upside down for about 15 seconds, then stopped. It works OK again now. In my earlier experience that's nothing unusual, so I tend to think you are wrong.
     
  13. Aug 31, 2010 #12

    sophiecentaur

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    I think that the rotating ball draws a small amount of air in and that "bubble' can lose the effect of the tension in the fluid ink so it stops flowing onto the paper.
    "Space Pens" and the patented Papermate 'pump' system keep a small amount of positive pressure inside which stops air being drawn in. So they work upside down more reliably.
     
  14. Aug 31, 2010 #13

    Borek

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    Could be - but as it works differently depending on the pen position, obviously gravity plays an important role.
     
  15. Aug 31, 2010 #14

    sophiecentaur

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    I wouldn't disagree with that but it's only of the same order as the other forces or else no ball point pen would work upside down(?). I imagine, for instance, that a pen with a very wide bore ink tube would be more susceptible (as, indeed, are normal 'ink' pens).
     
  16. Aug 31, 2010 #15

    Borek

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    We can do an international experiment - if anyone has a ball pen near by, please take a piece of paper and check how long the ball pen writes upside down :wink:
     
  17. Aug 31, 2010 #16
    The ball point pens are designed in such a way that the tiny ball does not allow any air flow inwards (sealed). If air had flown in through the nib, it would result in drying of ink which is not the case. How do you explain this?
     
  18. Aug 31, 2010 #17

    sophiecentaur

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    I agree with that, in principle, but, in practice, pens do stop writing and that has to be because a void forming behind the ball when inverted. In fact it takes a finite time (more than one rotation of the ball) to stop writing, which implies that the effect isn't just due to a sudden change in pressure. I thing this must imply that there must be some finite amount of air admitted. Remember, you don't need a lot- just enough to break the capillary attraction. I do know that cheap ball points need to be stored ball-down or they will dry / clog the ball and stop working permanently. It really is a brilliant bit of modern design, though, even down to the texture of the rolling ball surface and the consistency of the ink.
    As for the drying ink problem, the amount of air admitted would be very small -and only when the ball was rolling - so evaporation would be negligible.
    Fountain pens do dry and clog eventually and need to be flushed with more ink. Not that I've used one for a few decades.
     
  19. Aug 31, 2010 #18
    OK, well, my papermate disposable pen has a small air hole on it's side near the nib. The rear end of the external tube is sealed. I've also seen this on all clear plastic Bic pens we all know and love.
    The reason is, of course, simple. Writing removes ink which, in a sealed container, would eventually create a vacuum that would not allow any more ink flow.
     
  20. Aug 31, 2010 #19

    Danger

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    I've never figured out how "cartridge pens" overcame that. (Not that I've even seen one since 1967.) I don't know if they exist any more, but they were what we had to use in school when we switched up from pencils. The nib was like that of a fountain pen, but accepted a plastic tube of ink which plugged into the back of it. They weren't vented, but seemed to work until the cartridge was empty. Fountain pens avoided the problem by using a collapsable rubber bladder to hold the ink.
    I'm wondering if part of the reason for the hole in a Bic is based upon the same reason that caps on aerosol cans have a vent—to keep the cap from blowing off during transport to a higher altitude than that of the manufacturing site.
     
  21. Aug 31, 2010 #20
    Danger, I could be wrong, but I think that the sealed "cartridge pen" inserts are pressurized.
     
  22. Aug 31, 2010 #21

    Danger

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    I hadn't considered that possibility. Good thought. (In my defense, I was 11 years old the last time I used one. :redface:)
     
  23. Aug 31, 2010 #22
    Yeah, I was a young one too at that time.
    Perhaps some "pen" expert can jump in and explain it all to us!!
     
  24. Aug 31, 2010 #23
    Nothing better than some physics break when doing some biology labs :tongue:

    My pen (BIC of course:rolleyes:) wrote for about 7 seconds upside down. The interesting thing for me is that if I held the pen upside down for a minute, and then started to write upside down, it still did around 6 seconds.
    My guess cohesion and adhesion are the key point here.
     
  25. Aug 31, 2010 #24

    Danger

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    Interesting idea, Sakha. I'd always thought that it was purely a combination of gravity and capillary action, but you make good sense.
     
  26. Aug 31, 2010 #25
    I'm not sure but I think capillary action is very related to adhesion and cohesion, can anyone confirm this?
     
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