My son just asked me at dinner and I do not have an exact answer.
In: 7
How does your son drink the water through the straw?
He SUCKS on the straw, creating a vacuum (suction), and the water comes up because it’s being suctioned in. So if he puts his finger there, the finger won’t let the air in, maintaining the suction.
What is suction? Well, all of the air that’s above our heads is also pulled down by Earth’s gravity like everything else. So it creates pressure, like the pressure in a balloon. It’s about 14 pounds of pressure per each square inch of surface. It’s about half of what car tires have in them (36 PSI).
We live inside a balloon of air. We don’t feel it because we’re used to it, but if you go up in space you have to have a space suit to keep yourself “inside a pressurized balloon” like you’re used to on Earth.
Anyway, suction is less pressure than this “normal” air pressure.
So basically, the air actually pushes the water INTO the straw, if you create suction (less pressure) at the other end.
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