Something I noticed about eye droppers

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Discussion Overview

The discussion revolves around the behavior of eye droppers and pipettes when drawing liquid from a container, particularly focusing on the differences in liquid volume drawn based on the position of the dropper within the container. Participants explore the underlying physical principles and personal observations related to this phenomenon.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant observes that an eye dropper can draw more liquid when positioned at the bottom of a container compared to the middle, leading to confusion about the cause.
  • Another participant questions whether the squeezing technique of the dropper bulb was consistent in both scenarios.
  • A participant suggests that the pressure differential between the bottom and middle of the container is responsible for the increased volume drawn, explaining that atmospheric pressure pushes the liquid into the dropper.
  • One participant notes that similar behavior occurs with pipettes, requiring suction to be applied near the bottom to effectively draw liquid.
  • A later reply reiterates the explanation of pressure differences, mentioning that the pressure at the bottom of the liquid is greater and contributes to drawing more liquid into the dropper.
  • Another participant expresses uncertainty about the sufficiency of the pressure differential as an explanation, indicating a lack of consensus on the matter.

Areas of Agreement / Disagreement

Participants generally agree that pressure differentials play a role in the behavior of the dropper, but there is no consensus on the completeness or accuracy of the explanations provided. Some participants express uncertainty about the mechanics involved.

Contextual Notes

There are unresolved assumptions regarding the mechanics of liquid movement in relation to pressure differentials, and the discussion does not clarify the extent to which these principles apply across different scenarios.

Pengwuino
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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?
 
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Sounds kinda weird. Are you sure that you're squeezing the bulb the same way in both cases?
 
Yah, I was able to replicate it multiple times... pretty weird...
 
Sure... :rolleyes: You just had to come up with this after Clausius split. He'd probably know it right off.
 
whose clausius :D some sort of greek god?
 
Some of us think so. :biggrin:
 
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.
 
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.
 
Pengwuino said:
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?
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.
 
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  • #10
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.
I'm at work now, so as long as my boss isn't using this one, I should be okay.
 
  • #11
Yah i just realized this last night while i was trying to get to sleep, thanks anyways :P
 
  • #12
Sleep? You were going to sleep? What the hell were you thinking of?
 
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  • #13
it was 7am >:( ROAR!
 
  • #14
Alright, then... you're excused. Carry on.
 

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