Chemistry/Physics Pressure Questions?

Question

1. Why is it that when we put a straw in a cup full of water, and then put our finger over the top of the straw, the water gets caught in the straw?
2. Why is it that when we put one straw inside a cup of water and another outside of the cup, and we put both of the straw's ends in our mouth and suck, it is hard to drink the water?

(If you can please explain it in scientific terms, if not then that is okay)

Answer 1

1. When the end of the straw is open, the atmospheric pressure inside the straw balances the pressure on the water surface in the glass. When you put your finger over the end of the straw, you block the atmospheric pressure from entering the end of the straw, but the pressure on the water surface outside remains. When you lift the straw, that pressure forces the water up the straw.

2. To sip water up the straw the vacuum provided by sucking lifts the water up the straw (actually it's the air pressure that pushes the water up the straw). However, the other straw can let air in freely and prevent your lungs from developing the required negative pressure. To look at it another way, the air pressure has to lift the weight of water into the first straw, but there is no weight to lift in the open straw, so air moves in freely and fills your lungs as fast as they expand, so no vacuum is created.