How to discover how air pressure affects the operation of a drinking straw?
1) Please a straw in your mouth with the other end in the glass of water.
2) Place a second straw in your mouth, but do not place the other en in the water.
3) Attempt to drink from the first straw. Are you successful?
Science behind it.
You do not actually suck liquid through a straw. Air pressure pushing on the surface of a liquid forces liquid up the straw and into your mouth. SAY WHAT?
This happens when you reduce the pressure inside the straw by expanding your lungs. If atmospheric pressure is greater on the surface of the water then in the straw, then water will be forced up the straw.
In order for this to happen, the sir pressure in your mouth must first be reduced. By letting air into your mouth through the other straw, the pressure within your mouth can never be reduced to below atmospheric pressure.