Air pressure pushing from outside
How Does a Straw Work?
You do not pull the drink up. You remove air, and outside air pressure pushes it up.
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Step 1 of 5
Air presses on everything, hard.
The atmosphere pushes with about ten tonnes on every square metre. You do not feel it because it presses equally from all sides.
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Step 2 of 5
Sucking removes air, it does not pull liquid.
Expanding your chest lowers the pressure inside the straw. Nothing reaches down and grabs the drink.
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Step 3 of 5
Now the pressures are unequal.
Full atmospheric pressure pushes on the drink's surface while less pushes down inside the straw. Liquid moves towards the lower pressure.
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Step 4 of 5
A hole in the straw ruins it.
Air rushes in through the hole instead of the liquid rising, so the pressure difference never builds. Nothing comes up.
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Step 5 of 5
There is a hard limit.
Air pressure can only support about ten metres of water. No amount of sucking will lift a drink higher than that, ever.
This limit puzzled well-diggers for centuries — no pump could suck water up from below about ten metres.
The short version
A straw works because you lower the pressure inside and outside air pressure pushes the drink up — with a ten-metre ceiling.
Try it yourself
Poke a pinhole near the top of a straw and try to drink. It becomes almost impossible.
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