Answer
When drinking a liquid with the use of a straw, the pressure within the straw has to be less than the atmospheric pressure on the liquid in the cup. This makes it possible for the liquid to be pushed up through the straw.
Work Step by Step
When drinking a liquid with the use of a straw, the pressure within the straw has to be less than the atmospheric pressure on the liquid in the cup. This makes it possible for the liquid to be pushed up through the straw.