How does a straw let you drink?
Let me show you who is really doing the work, in 30 seconds.A straw works not because your mouth pulls the drink up, but because the air around it pushes the drink up. When you suck out some of the air inside the straw, the push from inside gets weaker. Then the air pressing on the surface of the drink in the cup pushes the drink up into the straw.
Air is always pushing
The air around us has weight, and it presses on everything on the ground. When a straw is simply standing in a cup, the air presses equally on the drink inside the straw and on the drink in the cup, so the drink inside stays at the same level as the drink outside.
Sucking creates a difference in push
When you put the straw in your mouth and suck, there is less air in your mouth and in the straw, so the push on the drink from above inside the straw gets weaker. Now the outside air pressing on the surface of the drink in the cup is stronger, and the drink is pushed up through the straw. The more air you remove, the bigger the difference, and the higher the drink rises.
About 10 meters is the limit
There is a limit to how high the outside air can push. Even if you removed all the air from inside the straw, at sea level the air could only push water up to about 10.3 meters. If the straw reached higher than that, the water would never get to your mouth, no matter how hard you sucked. In real life, you can't completely empty the air from your mouth, so the height a person can actually drink from is much lower.
Even lower in high places
In places with lower air pressure, such as high in the mountains, the air pushes with less force, so it can't push the drink up as high. In Colorado, a high-altitude state in the United States, it has been said that you can no longer drink through a straw that is about 9 meters tall.
Want to know more?
- What matters is not how long the straw is, but how high the drink has to be lifted. If you lay a very long straw almost flat, you can still drink through it.
- A barometer uses the same idea: it measures the push of the air by the height of a liquid in a tube. Using mercury, which is heavier than water, lets the tube be much shorter.
Quick quiz: test yourself
What makes a drink rise up a straw?
Show the answer
- Your mouth pulling it up
- The drink's surface tension
- The surrounding air pushing it
The surrounding air pushing it Sucking removes air from the straw, so the outside air pressing on the drink's surface pushes the drink up into the straw.
Sucking removes air from the straw, so the outside air pressing on the drink's surface pushes the drink up into the straw.
Next quiz ›Sources
- Can you drink through a 30 foot straw?Little Shop of Physics, Colorado State University（コロラド州立大学）
- A Really Long StrawScientific American（Science Buddies）
This article was written after checking the sources above as of 2026-10-03. Explanations may change as research progresses. Photo credits are shown below each photo.
