How does a normal pipette work?

[sameeralord]

Main Question or Discussion Point

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

 

[Borek]

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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[sameeralord]

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?

 

[Borek]

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.

 

[sameeralord]

Ok I see it was a simple question after all. Thanks for the help Borek.