How does the sucking action of a straw work?
n order to make a straw work you have to put the straw in your mouth and inhale. When you inhale your soft palate (on the roof of your mouth) rises, leaving an empty space inside your mouth. Since that empty space needs to be filled the air in the straw starts coming up and into your mouth followed by the liquid from your cup filling the empty space. You then are able to drink the liquid.
This is all thanks to Air pressure and water pressure. Lets say that you are drinking water from a glass with the help of a straw. When you suck at the straw, you are essentially drawing air out of the straw. This decreases air pressure which was in the straw right above the level of the water. In the mean time the air pressure around your glass of water is constantly pushing the drink level to go down. And the water pressure of your drink is pushing the water level to go up. Since you just helped decrease the air pressure in the straw, the water finds an outlet and thus goes up the straw till it reaches your mouth.
