This is the critter spray gun. enter image description here

The liquid in the jar is at atmospheric pressure (there's a vent hole connecting it to the atmosphere). A fast jet of air flowing right over the end of the pickup tube sucks the liquid up the tube and into the air stream. How exactly does this fast stream of air creates suction? It's released in the atmosphere, so shouldn't it also be at atmospheric pressure?

enter image description here


this is called an aspirator pump. By blowing a jet of air across the top of the dip tube, a slight negative pressure is developed there and the air in the end of the dip tube is thus urged to join in the flow. This draws fluid up the tube which then gets dispersed into the jet.

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  • $\begingroup$ Yes but how, niels? $\endgroup$ – Tom B. Mar 21 '18 at 0:33
  • $\begingroup$ @tomb, there is a law of fluid dynamics called Bernoulli's law, which states that fluid flow across a surface exerts a negative pressure on that surface. this is the source of the suction that pulls fluid up the dip tube and releases it into the jet of air. $\endgroup$ – niels nielsen Mar 21 '18 at 1:32
  • $\begingroup$ I know that principal. I was hoping an answer would unpack it. With respect, your answer restates a phenomenon described in the question, and you give it a name in the comment. Note, it's not personal, I've read several satisfying answers of yours in the past. I think it's time I do more research and get to the bottom of Bernoulli once and for all because it's bothered me for awhile. $\endgroup$ – Tom B. Mar 21 '18 at 4:44
  • $\begingroup$ @tomb, agree, bernoulli has puzzled me for years and I cannot derive it for you from fundamental principles- I hope someone else can, if you get a good explanation in your research please share it here. best regards, niels $\endgroup$ – niels nielsen Mar 21 '18 at 7:50

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