How does a normal pipette work?

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A normal pipette operates by creating a pressure difference when the top is squeezed. Squeezing the pipette expels air, and when it is submerged in liquid and released, the rubber returns to its original shape, creating a low-pressure area that draws liquid into the pipette. The sequence of squeezing before or after submersion does not affect the suction process; the key is the pressure difference created inside the pipette. Understanding this mechanism clarifies how pipettes function effectively in liquid transfer. This discussion highlights the basic principles of fluid dynamics in pipette operation.
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Hello guys,

This might seem a basic question but my physics is not that good. So in a normal pipette when you squeeze the top bit, do you create an area of high pressure there, and then when you put in a flask with liquid and release it the air escapes, and then the atmospheric air pushes on the liquid and fluid comes into the pipette. Is that what happens? Thanks :smile:
 
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Air escapes when you squeeze, regardless of whether you have already put pipette in liquid or not. Other than that seems to me you are right.

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Hello Borek long time,

Ok thanks for the reply. Then why do some people keep the pipette squeezed and then put it into liquid and then release it to get the liquid. When you keep it squeezed haven't you already released the air? So how is air released again when you release it?
 
There is no difference. Important moment is when pipette is submerged and squezzed. When you stop squeezing rubber creates lower pressure and sucks the liquid. Lower pressure inside, higher pressure on the outside. Whether air left the pipette before it was submerged or after doesn't change the sucking part.
 
Ok I see it was a simple question after all. Thanks for the help Borek.
 

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