How does water stay in a straw when you place your finger over the opposite opening?

Question

My son just asked me at dinner and I do not have an exact answer.

In: 7

Answer 1

If the water should sink, something had to take its place. But since your’re holding your finger over one end, and the other end is sealed in water, no air can enter the straw. So the water cannot sink down to its normal level.