My physics teacher told me...

This shows how slippery words can be. There actually isn’t any suction or sucking going on in physics. What it is, is a pressure differential. When you “suck” (common usage) you are INCREASING the volume of the cavity you call your mouth (and lungs). This increase causes the pressure inside your mouth to decrease. The difference in pressure of the interior of your mouth and the atmosphere we live in, causes the atmospheric pressure to force liquid up the straw until pressure is equalized. Periodic swallowing keeps the pressure differential in place.

If you had a rigid, leak-proof straw that was longer than 35 feet, you could NEVER get water out of the top of the straw by “sucking” because atmospheric pressure is only great enough to raise it 33.9 feet. Mercury, being denser, would be restricted to a height of 29.9 inches. (Both are plus or minus a bit to account for local variations. That is why in weather forecasts in the US, they always talk about the pressure falling/rising as inches of mercury.)

Hope this helps. Good Luck !!

p.s. In physics, there also is no such thing as centrifugal force, like what is thought of while on a fast merry-go-round.